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Signed-off-by: Juri Lelli <juri.lelli@arm.com>
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With energy-aware scheduling enabled nohz_kick_needed() generates many
nohz idle-balance kicks which lead to nothing when multiple tasks get
packed on a single cpu to save energy. This causes unnecessary wake-ups
and hence wastes energy. Make these conditions depend on !energy_aware()
for now until the energy-aware nohz story gets sorted out.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Add an extra criteria to need_active_balance() to kick off active load
balance if the source cpu is overutilized and has lower capacity than
the destination cpus.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Skip cpu as a potential src (costliest) in case it has only one task
running and its original capacity is greater than or equal to the
original capacity of the dst cpu.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
[major changes: Juri Lelli]
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Energy-aware load balancing bases on cpu usage so the upper bound of its
operational range is a fully utilized cpu. Above this tipping point it
makes more sense to use weighted_cpuload to preserve smp_nice.
This patch implements the tipping point detection in update_sg_lb_stats
as if one cpu is over-utilized the current energy-aware load balance
operation will fall back into the conventional weighted load based one.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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Energy-aware load balancing does not rely on env->imbalance but instead it
evaluates the system-wide energy difference for each task on the src rq by
potentially moving it to the dst rq. If this energy difference is lesser
than zero the task is actually moved from src to dst rq.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
[major change in move_tasks(): Juri Lelli]
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In case that after the gathering of sched domain statistics the current
load balancing operation is still in energy-aware mode and a least
efficient sched group has been found, detect the least efficient cpu by
comparing the cpu efficiency (ratio between cpu usage and cpu energy
consumption) among all cpus of the least efficient sched group.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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In case that after the gathering of sched domain statistics the current
load balancing operation is still in energy-aware mode, just return the
least efficient (costliest) reference. That implies the system is
considered to be balanced in case no least efficient sched group was
found.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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Energy-aware load balancing has to work alongside the conventional load
based functionality. This includes the tipping point feature, i.e. being
able to fall back from energy aware to the conventional load based
functionality during an ongoing load balancing action.
That is why this patch introduces an additional reference to hold the
least efficient sched group (costliest) as well its statistics in form of
an extra sg_lb_stats structure (costliest_stat).
The function update_sd_pick_costliest is used to assign the least
efficient sched group parallel to the existing update_sd_pick_busiest.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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To be able to identify the least efficient (costliest) sched group
introduce group_eff as the efficiency of the sched group into sg_lb_stats.
The group efficiency is defined as the ratio between the group usage and
the group energy consumption.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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Energy-aware load balancing should only happen if the ENERGY_AWARE feature
is turned on and the sched domain on which the load balancing is performed
on contains energy data.
There is also a need during a load balance action to be able to query if we
should continue to load balance energy-aware or if we reached the tipping
point which forces us to fall back to the conventional load balancing
functionality.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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Make wake-ups of new tasks (find_idlest_group) aware of any differences
in cpu compute capacity so new tasks don't get handed off to a cpus with
lower capacity.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Let available compute capacity and estimated energy impact select
wake-up target cpu when energy-aware scheduling is enabled.
energy_aware_wake_cpu() attempts to find group of cpus with sufficient
compute capacity to accommodate the task and find a cpu with enough spare
capacity to handle the task within that group. Preference is given to
cpus with enough spare capacity at the current OPP. Finally, the energy
impact of the new target and the previous task cpu is compared to select
the wake-up target cpu.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Adds a generic energy-aware helper function, energy_diff(), that
calculates energy impact of adding, removing, and migrating utilization
in the system.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Extended sched_group_energy() to support energy prediction with usage
(tasks) added/removed from a specific cpu or migrated between a pair of
cpus. Useful for load-balancing decision making.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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For energy-aware load-balancing decisions it is necessary to know the
energy consumption estimates of groups of cpus. This patch introduces a
basic function, sched_group_energy(), which estimates the energy
consumption of the cpus in the group and any resources shared by the
members of the group.
NOTE: The function has five levels of identation and breaks the 80
character limit. Refactoring is necessary.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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With scale-invariant usage tracking get_cpu_usage() should never return
a usage above the current compute capacity of the cpu (capacity_curr).
The scaling of the utilization tracking contributions should generally
cause the cpu utilization to saturate at capacity_curr, but it may
temporarily exceed this value in certain situations. This patch changes
the cap from capacity_orig to capacity_curr.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Move get_cpu_usage() to an earlier position in fair.c.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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capacity_orig_of() returns the max available compute capacity of a cpu.
For scale-invariant utilization tracking and energy-aware scheduling
decisions it is useful to know the compute capacity available at the
current OPP of a cpu.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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This patch introduces the ENERGY_AWARE sched feature, which is
implemented using jump labels when SCHED_DEBUG is defined. It is
statically set false when SCHED_DEBUG is not defined. Hence this doesn't
allow energy awareness to be enabled without SCHED_DEBUG. This
sched_feature knob will be replaced later with a more appropriate
control knob when things have matured a bit.
ENERGY_AWARE is based on per-entity load-tracking hence FAIR_GROUP_SCHED
must be enable. This dependency isn't checked at compile time yet.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Add the blocked utilization contribution to group sched_entity
utilization (se->avg.utilization_avg_contrib) and to get_cpu_usage().
With this change cpu usage now includes recent usage by currently
non-runnable tasks, hence it provides a more stable view of the cpu
usage. It does, however, also mean that the meaning of usage is changed:
A cpu may be momentarily idle while usage >0. It can no longer be
assumed that cpu usage >0 implies runnable tasks on the rq.
cfs_rq->utilization_load_avg or nr_running should be used instead to get
the current rq status.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Introduces the blocked utilization, the utilization counter-part to
cfs_rq->utilization_load_avg. It is the sum of sched_entity utilization
contributions of entities that were recently on the cfs_rq that are
currently blocked. Combined with sum of contributions of entities
currently on the cfs_rq or currently running
(cfs_rq->utilization_load_avg) this can provide a more stable average
view of the cpu usage.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
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Since now we have besides frequency invariant also cpu (uarch plus max
system frequency) invariant cfs_rq::utilization_load_avg both, frequency
and cpu scaling happens as part of the load tracking.
So cfs_rq::utilization_load_avg does not have to be scaled by the original
capacity of the cpu again.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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Besides the existing frequency scale-invariance correction factor, apply
cpu scale-invariance correction factor to usage tracking.
Cpu scale-invariance takes cpu performance deviations due to
micro-architectural differences (i.e. instructions per seconds) between
cpus in HMP systems (e.g. big.LITTLE) and differences in the frequency
value of the highest OPP between cpus in SMP systems into consideration.
Each segment of the sched_avg::running_avg_sum geometric series is now
scaled by the cpu performance factor too so the
sched_avg::utilization_avg_contrib of each entity will be invariant from
the particular cpu of the HMP/SMP system it is gathered on.
So the usage level that is returned by get_cpu_usage stays relative to
the max cpu performance of the system.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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Apply frequency scale-invariance correction factor to load tracking.
Each segment of the sched_avg::runnable_avg_sum geometric series is now
scaled by the current frequency so the sched_avg::load_avg_contrib of each
entity will be invariant with frequency scaling. As a result,
cfs_rq::runnable_load_avg which is the sum of sched_avg::load_avg_contrib,
becomes invariant too. So the load level that is returned by
weighted_cpuload, stays relative to the max frequency of the cpu.
Then, we want the keep the load tracking values in a 32bits type, which
implies that the max value of sched_avg::{runnable|running}_avg_sum must
be lower than 2^32/88761=48388 (88761 is the max weight of a task). As
LOAD_AVG_MAX = 47742, arch_scale_freq_capacity must return a value less
than (48388/47742) << SCHED_CAPACITY_SHIFT = 1037 (SCHED_SCALE_CAPACITY =
1024). So we define the range to [0..SCHED_SCALE_CAPACITY] in order to
avoid overflow.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
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When a CPU is used to handle a lot of IRQs or some RT tasks, the remaining
capacity for CFS tasks can be significantly reduced. Once we detect such
situation by comparing cpu_capacity_orig and cpu_capacity, we trig an idle
load balance to check if it's worth moving its tasks on an idle CPU.
Once the idle load_balance has selected the busiest CPU, it will look for an
active load balance for only two cases :
- there is only 1 task on the busiest CPU.
- we haven't been able to move a task of the busiest rq.
A CPU with a reduced capacity is included in the 1st case, and it's worth to
actively migrate its task if the idle CPU has got full capacity. This test has
been added in need_active_balance.
As a sidenote, this will note generate more spurious ilb because we already
trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that
has a task, we will trig the ilb once for migrating the task.
The nohz_kick_needed function has been cleaned up a bit while adding the new
test
env.src_cpu and env.src_rq must be set unconditionnally because they are used
in need_active_balance which is called even if busiest->nr_running equals 1
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
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The scheduler tries to compute how many tasks a group of CPUs can handle by
assuming that a task's load is SCHED_LOAD_SCALE and a CPU's capacity is
SCHED_CAPACITY_SCALE. group_capacity_factor divides the capacity of the group
by SCHED_LOAD_SCALE to estimate how many task can run in the group. Then, it
compares this value with the sum of nr_running to decide if the group is
overloaded or not. But the group_capacity_factor is hardly working for SMT
system, it sometimes works for big cores but fails to do the right thing for
little cores.
Below are two examples to illustrate the problem that this patch solves:
1- If the original capacity of a CPU is less than SCHED_CAPACITY_SCALE
(640 as an example), a group of 3 CPUS will have a max capacity_factor of 2
(div_round_closest(3x640/1024) = 2) which means that it will be seen as
overloaded even if we have only one task per CPU.
2 - If the original capacity of a CPU is greater than SCHED_CAPACITY_SCALE
(1512 as an example), a group of 4 CPUs will have a capacity_factor of 4
(at max and thanks to the fix [0] for SMT system that prevent the apparition
of ghost CPUs) but if one CPU is fully used by rt tasks (and its capacity is
reduced to nearly nothing), the capacity factor of the group will still be 4
(div_round_closest(3*1512/1024) = 5 which is cap to 4 with [0]).
So, this patch tries to solve this issue by removing capacity_factor and
replacing it with the 2 following metrics :
-The available CPU's capacity for CFS tasks which is already used by
load_balance.
-The usage of the CPU by the CFS tasks. For the latter, utilization_avg_contrib
has been re-introduced to compute the usage of a CPU by CFS tasks.
group_capacity_factor and group_has_free_capacity has been removed and replaced
by group_no_capacity. We compare the number of task with the number of CPUs and
we evaluate the level of utilization of the CPUs to define if a group is
overloaded or if a group has capacity to handle more tasks.
For SD_PREFER_SIBLING, a group is tagged overloaded if it has more than 1 task
so it will be selected in priority (among the overloaded groups). Since [1],
SD_PREFER_SIBLING is no more concerned by the computation of load_above_capacity
because local is not overloaded.
Finally, the sched_group->sched_group_capacity->capacity_orig has been removed
because it's no more used during load balance.
[1] https://lkml.org/lkml/2014/8/12/295
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
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Monitor the usage level of each group of each sched_domain level. The usage is
the portion of cpu_capacity_orig that is currently used on a CPU or group of
CPUs. We use the utilization_load_avg to evaluate the usage level of each
group.
The utilization_load_avg only takes into account the running time of the CFS
tasks on a CPU with a maximum value of SCHED_LOAD_SCALE when the CPU is fully
utilized. Nevertheless, we must cap utilization_load_avg which can be temporaly
greater than SCHED_LOAD_SCALE after the migration of a task on this CPU and
until the metrics are stabilized.
The utilization_load_avg is in the range [0..SCHED_LOAD_SCALE] to reflect the
running load on the CPU whereas the available capacity for the CFS task is in
the range [0..cpu_capacity_orig]. In order to test if a CPU is fully utilized
by CFS tasks, we have to scale the utilization in the cpu_capacity_orig range
of the CPU to get the usage of the latter. The usage can then be compared with
the available capacity (ie cpu_capacity) to deduct the usage level of a CPU.
The frequency scaling invariance of the usage is not taken into account in this
patch, it will be solved in another patch which will deal with frequency
scaling invariance on the running_load_avg.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
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This new field cpu_capacity_orig reflects the original capacity of a CPU
before being altered by rt tasks and/or IRQ
The cpu_capacity_orig will be used:
- to detect when the capacity of a CPU has been noticeably reduced so we can
trig load balance to look for a CPU with better capacity. As an example, we
can detect when a CPU handles a significant amount of irq
(with CONFIG_IRQ_TIME_ACCOUNTING) but this CPU is seen as an idle CPU by
scheduler whereas CPUs, which are really idle, are available.
- evaluate the available capacity for CFS tasks
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
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The average running time of RT tasks is used to estimate the remaining compute
capacity for CFS tasks. This remaining capacity is the original capacity scaled
down by a factor (aka scale_rt_capacity). This estimation of available capacity
must also be invariant with frequency scaling.
A frequency scaling factor is applied on the running time of the RT tasks for
computing scale_rt_capacity.
In sched_rt_avg_update, we scale the RT execution time like below:
rq->rt_avg += rt_delta * arch_scale_freq_capacity() >> SCHED_CAPACITY_SHIFT
Then, scale_rt_capacity can be summarized by:
scale_rt_capacity = SCHED_CAPACITY_SCALE -
((rq->rt_avg << SCHED_CAPACITY_SHIFT) / period)
We can optimize by removing right and left shift in the computation of rq->rt_avg
and scale_rt_capacity
The call to arch_scale_frequency_capacity in the rt scheduling path might be
a concern for RT folks because I'm not sure whether we can rely on
arch_scale_freq_capacity to be short and efficient ?
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
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Apply frequency scale-invariance correction factor to usage tracking.
Each segment of the running_load_avg geometric series is now scaled by the
current frequency so the utilization_avg_contrib of each entity will be
invariant with frequency scaling. As a result, utilization_load_avg which is
the sum of utilization_avg_contrib, becomes invariant too. So the usage level
that is returned by get_cpu_usage, stays relative to the max frequency as the
cpu_capacity which is is compared against.
Then, we want the keep the load tracking values in a 32bits type, which implies
that the max value of {runnable|running}_avg_sum must be lower than
2^32/88761=48388 (88761 is the max weigth of a task). As LOAD_AVG_MAX = 47742,
arch_scale_freq_capacity must return a value less than
(48388/47742) << SCHED_CAPACITY_SHIFT = 1037 (SCHED_SCALE_CAPACITY = 1024).
So we define the range to [0..SCHED_SCALE_CAPACITY] in order to avoid overflow.
cc: Paul Turner <pjt@google.com>
cc: Ben Segall <bsegall@google.com>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
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Now that arch_scale_cpu_capacity has been introduced to scale the original
capacity, the arch_scale_freq_capacity is no longer used (it was
previously used by ARM arch). Remove arch_scale_freq_capacity from the
computation of cpu_capacity. The frequency invariance will be handled in the
load tracking and not in the CPU capacity. arch_scale_freq_capacity will be
revisited for scaling load with the current frequency of the CPUs in a later
patch.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
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Adds usage contribution tracking for group entities. Unlike
se->avg.load_avg_contrib, se->avg.utilization_avg_contrib for group
entities is the sum of se->avg.utilization_avg_contrib for all entities on the
group runqueue. It is _not_ influenced in any way by the task group
h_load. Hence it is representing the actual cpu usage of the group, not
its intended load contribution which may differ significantly from the
utilization on lightly utilized systems.
cc: Paul Turner <pjt@google.com>
cc: Ben Segall <bsegall@google.com>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
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Add new statistics which reflect the average time a task is running on the CPU
and the sum of these running time of the tasks on a runqueue. The latter is
named utilization_load_avg.
This patch is based on the usage metric that was proposed in the 1st
versions of the per-entity load tracking patchset by Paul Turner
<pjt@google.com> but that has be removed afterwards. This version differs from
the original one in the sense that it's not linked to task_group.
The rq's utilization_load_avg will be used to check if a rq is overloaded or
not instead of trying to compute how many tasks a group of CPUs can handle.
Rename runnable_avg_period into avg_period as it is now used with both
runnable_avg_sum and running_avg_sum
Add some descriptions of the variables to explain their differences
cc: Paul Turner <pjt@google.com>
cc: Ben Segall <bsegall@google.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
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The capacity of a CPU/group should be some intrinsic value that doesn't
change with task placement. It is like a container which capacity is
stable regardless of the amount of liquid in it (its "utilization")...
unless the container itself is crushed that is, but that's another story.
Therefore let's rename "has_capacity" to "has_free_capacity" in order to
better convey the wanted meaning.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: linaro-kernel@lists.linaro.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/n/tip-djzkk027jm0e8x8jxy70opzh@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 1b6a7495d343fcfe22ff3a8285544bb8e40f1920)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Conflicts:
kernel/sched/fair.c
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Combine two branches which do the same.
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140922183612.11015.64200.stgit@localhost
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 7a96c231ca23f0f5622852307df4209afc502ec3)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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This patch favours moving tasks towards NUMA node that recorded a higher
number of NUMA faults during active load balancing. Ideally this is
self-reinforcing as the longer the task runs on that node, the more faults
it should incur causing task_numa_placement to keep the task running on that
node. In reality a big weakness is that the nodes CPUs can be overloaded
and it would be more efficient to queue tasks on an idle node and migrate
to the new node. This would require additional smarts in the balancer so
for now the balancer will simply prefer to place the task on the preferred
node for a PTE scans which is controlled by the numa_balancing_settle_count
sysctl. Once the settle_count number of scans has complete the schedule
is free to place the task on an alternative node if the load is imbalanced.
[srikar@linux.vnet.ibm.com: Fixed statistics]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
[ Tunable and use higher faults instead of preferred. ]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-23-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 3a7053b3224f4a8b0e8184166190076593621617)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Conflicts:
Documentation/sysctl/kernel.txt
include/linux/sched.h
kernel/sched/core.c
kernel/sched/fair.c
kernel/sched/features.h
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Currently the task always wakes affine on this_cpu if the latter is idle.
Before waking up the task on this_cpu, we check that this_cpu capacity is not
significantly reduced because of RT tasks or irq activity.
Use case where the number of irq and/or the time spent under irq is important
will take benefit of this because the task that is woken up by irq or softirq
will not use the same CPU than irq (and softirq) but a idle one.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-8-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit bd61c98f9b3f142cd63f9e15acfe203bec9e5f5a)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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The computation of avg_load and avg_load_per_task should only take into
account the number of CFS tasks. The non-CFS tasks are already taken into
account by decreasing the CPU's capacity and they will be tracked in the
CPU's utilization (group_utilization) of the next patches.
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-4-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 65fdac08c264506ff95ee1e34ae066e308c9e6e3)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Conflicts:
kernel/sched/fair.c
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In wake_affine() I have tried to understand the meaning of the condition:
(this_load <= load &&
this_load + target_load(prev_cpu, idx) <= tl_per_task)
but I failed to find a use case that can take advantage of it and I haven't
found clear description in the previous commit's log.
Futhermore, the comment of the condition refers to the task_hot function that
was used before being replaced by the current condition:
/*
* This domain has SD_WAKE_AFFINE and
* p is cache cold in this domain, and
* there is no bad imbalance.
*/
If we look more deeply the below condition:
this_load + target_load(prev_cpu, idx) <= tl_per_task
When sync is clear, we have:
tl_per_task = runnable_load_avg / nr_running
this_load = max(runnable_load_avg, cpuload[idx])
target_load = max(runnable_load_avg', cpuload'[idx])
It implies that runnable_load_avg == 0 and nr_running <= 1 in order to match the
condition. This implies that runnable_load_avg == 0 too because of the
condition: this_load <= load.
but if this _load is null, 'balanced' is already set and the test is redundant.
If sync is set, it's not as straight forward as above (especially if cgroup
are involved) but the policy should be similar as we have removed a task that's
going to sleep in order to get a more accurate load and this_load values.
The current conclusion is that these additional condition don't give any benefit
so we can remove them.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-3-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 05bfb65f52cbdabe26ebb629959416a6cffb034d)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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The imbalance flag can stay set whereas there is no imbalance.
Let assume that we have 3 tasks that run on a dual cores /dual cluster system.
We will have some idle load balance which are triggered during tick.
Unfortunately, the tick is also used to queue background work so we can reach
the situation where short work has been queued on a CPU which already runs a
task. The load balance will detect this imbalance (2 tasks on 1 CPU and an idle
CPU) and will try to pull the waiting task on the idle CPU. The waiting task is
a worker thread that is pinned on a CPU so an imbalance due to pinned task is
detected and the imbalance flag is set.
Then, we will not be able to clear the flag because we have at most 1 task on
each CPU but the imbalance flag will trig to useless active load balance
between the idle CPU and the busy CPU.
We need to reset of the imbalance flag as soon as we have reached a balanced
state. If all tasks are pinned, we don't consider that as a balanced state and
let the imbalance flag set.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-2-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit afdeee0510db918b31bb4aba47452df2ddbdbcf2)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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'capacity_orig' is only changed for systems with an SMT sched_domain level in order
to reflect the lower capacity of CPUs. Heterogenous systems also have to reflect an
original capacity that is different from the default value.
Create a more generic function arch_scale_cpu_capacity that can be also used by
non SMT platforms to set capacity_orig.
The __weak implementation of arch_scale_cpu_capacity() is the previous SMT variant,
in order to keep backward compatibility with the use of capacity_orig.
arch_scale_smt_capacity() and default_scale_smt_capacity() have been removed as
they were not used elsewhere than in arch_scale_cpu_capacity().
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Reviewed-by: Preeti U. Murthy <preeti@linux.vnet.ibm.com>
[ Added default_scale_cpu_capacity() back. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-5-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 26bc3c50d3b3984564c270da86f1fbbfb774dbcd)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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Since commit caeb178c60f4 ("sched/fair: Make update_sd_pick_busiest() ...")
sd_pick_busiest returns a group that can be neither imbalanced nor overloaded
but is only more loaded than others. This change has been introduced to ensure
a better load balance in system that are not overloaded but as a side effect,
it can also generate useless active migration between groups.
Let take the example of 3 tasks on a quad cores system. We will always have an
idle core so the load balance will find a busiest group (core) whenever an ILB
is triggered and it will force an active migration (once above
nr_balance_failed threshold) so the idle core becomes busy but another core
will become idle. With the next ILB, the freshly idle core will try to pull the
task of a busy CPU.
The number of spurious active migration is not so huge in quad core system
because the ILB is not triggered so much. But it becomes significant as soon as
you have more than one sched_domain level like on a dual cluster of quad cores
where the ILB is triggered every tick when you have more than 1 busy_cpu
We need to ensure that the migration generate a real improveùent and will not
only move the avg_load imbalance on another CPU.
Before caeb178c60f4f93f1b45c0bc056b5cf6d217b67f, the filtering of such use
case was ensured by the following test in f_b_g:
if ((local->idle_cpus < busiest->idle_cpus) &&
busiest->sum_nr_running <= busiest->group_weight)
This patch modified the condition to take into account situation where busiest
group is not overloaded: If the diff between the number of idle cpus in 2
groups is less than or equal to 1 and the busiest group is not overloaded,
moving a task will not improve the load balance but just move it.
A test with sysbench on a dual clusters of quad cores gives the following
results:
command: sysbench --test=cpu --num-threads=5 --max-time=5 run
The HZ is 200 which means that 1000 ticks has fired during the test.
With Mainline, perf gives the following figures:
Samples: 727 of event 'sched:sched_migrate_task'
Event count (approx.): 727
Overhead Command Shared Object Symbol
........ ............... ............. ..............
12.52% migration/1 [unknown] [.] 00000000
12.52% migration/5 [unknown] [.] 00000000
12.52% migration/7 [unknown] [.] 00000000
12.10% migration/6 [unknown] [.] 00000000
11.83% migration/0 [unknown] [.] 00000000
11.83% migration/3 [unknown] [.] 00000000
11.14% migration/4 [unknown] [.] 00000000
10.87% migration/2 [unknown] [.] 00000000
2.75% sysbench [unknown] [.] 00000000
0.83% swapper [unknown] [.] 00000000
0.55% ktps65090charge [unknown] [.] 00000000
0.41% mmcqd/1 [unknown] [.] 00000000
0.14% perf [unknown] [.] 00000000
With this patch, perf gives the following figures
Samples: 20 of event 'sched:sched_migrate_task'
Event count (approx.): 20
Overhead Command Shared Object Symbol
........ ............... ............. ..............
80.00% sysbench [unknown] [.] 00000000
10.00% swapper [unknown] [.] 00000000
5.00% ktps65090charge [unknown] [.] 00000000
5.00% migration/1 [unknown] [.] 00000000
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1412170735-5356-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 43f4d66637bc752e93a77ff2536474a5a3888442)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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The code in find_idlest_cpu() looks for the CPU with the smallest load.
However, if multiple CPUs are idle, the first idle CPU is selected
irrespective of the depth of its idle state.
Among the idle CPUs we should pick the one with with the shallowest idle
state, or the latest to have gone idle if all idle CPUs are in the same
state. The later applies even when cpuidle is configured out.
This patch doesn't cover the following issues:
- The idle exit latency of a CPU might be larger than the time needed
to migrate the waking task to an already running CPU with sufficient
capacity, and therefore performance would benefit from task packing
in such case (in most cases task packing is about power saving).
- Some idle states have a non negligible and non abortable entry latency
which needs to run to completion before the exit latency can start.
A concurrent patch series is making this info available to the cpuidle
core. Once available, the entry latency with the idle timestamp could
determine when the exit latency may be effective.
Those issues will be handled in due course. In the mean time, what
is implemented here should improve things already compared to the current
state of affairs.
Based on an initial patch from Daniel Lezcano.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-pm@vger.kernel.org
Cc: linaro-kernel@lists.linaro.org
Link: http://lkml.kernel.org/n/tip-@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 83a0a96a5f26d974580fd7251043ff70c8f1823d)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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(sched_entity::on_rq == 1) does not guarantee the task is pickable;
changes on throttled cfs_rq must not lead to reschedule.
Check for task_struct::on_rq instead.
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1407312361.8424.35.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit f36c019c79edb3a89920afae1b2b45987af1a112)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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Allow calculate_imbalance() to 'create' idle cpus in the busiest group
if there are idle cpus in the local group.
Suggested-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140729152705.GX12054@laptop.lan
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 9a5d9ba6a3631d55c358fe1bdbaa162a97471a05)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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Currently update_sd_pick_busiest only identifies the busiest sd
that is either overloaded, or has a group imbalance. When no
sd is imbalanced or overloaded, the load balancer fails to find
the busiest domain.
This breaks load balancing between domains that are not overloaded,
in the !SD_ASYM_PACKING case. This patch makes update_sd_pick_busiest
return true when the busiest sd yet is encountered.
Groups are ranked in the order overloaded > imbalanced > other,
with higher ranked groups getting priority even when their load
is lower. This is necessary due to the possibility of unequal
capacities and cpumasks between domains within a sched group.
Behaviour for SD_ASYM_PACKING does not seem to match the comment,
but I have no hardware to test that so I have left the behaviour
of that code unchanged.
Enum for group classification suggested by Peter Zijlstra.
Signed-off-by: Rik van Riel <riel@redhat.com>
[peterz: replaced sg_lb_stats::group_imb with the new enum group_type
in an attempt to avoid endless recalculation]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Michael Neuling <mikey@neuling.org>
Cc: ktkhai@parallels.com
Cc: tim.c.chen@linux.intel.com
Cc: nicolas.pitre@linaro.org
Cc: jhladky@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140729152743.GI3935@laptop
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit caeb178c60f4f93f1b45c0bc056b5cf6d217b67f)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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Rik noticed that calculate_imbalance() relies on
update_sd_pick_busiest() to guarantee that busiest->sum_nr_running >
busiest->group_capacity_factor.
Break this implicit assumption (with the intent of not providing it
anymore) by having calculat_imbalance() verify it and not rely on
others.
Reported-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20140729152631.GW12054@laptop.lan
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 743cb1ff191f00fee653212bdbcee1e56086d6ce)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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When computing cache hot, we should check if the migration dst cpu is idle,
instead of the current cpu. Though they are same in normal balancing, that
is false nowadays in nohz idle balancing at least.
Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Mike Galbraith <mgalbraith@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140607090452.4696E301D2@webmail.sinamail.sina.com.cn
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 5d5e2b1bcbdc996e72815c03fdc5ea82c4642397)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Conflicts:
kernel/sched/fair.c
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It is better not to think about compute capacity as being equivalent
to "CPU power". The upcoming "power aware" scheduler work may create
confusion with the notion of energy consumption if "power" is used too
liberally.
Let's rename the following feature flags since they do relate to capacity:
SD_SHARE_CPUPOWER -> SD_SHARE_CPUCAPACITY
ARCH_POWER -> ARCH_CAPACITY
NONTASK_POWER -> NONTASK_CAPACITY
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: linaro-kernel@lists.linaro.org
Cc: Andy Fleming <afleming@freescale.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/n/tip-e93lpnxb87owfievqatey6b5@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 5d4dfddd4f02b028d6ddaaa04d75d3b0cad1c9ae)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
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