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In init.rc, there are following settings related cpuctl
# Create cgroup mount points for process groups
mkdir /dev/cpuctl
mount cgroup none /dev/cpuctl cpu
chown system system /dev/cpuctl
chown system system /dev/cpuctl/tasks
chmod 0666 /dev/cpuctl/tasks
write /dev/cpuctl/cpu.shares 1024
write /dev/cpuctl/cpu.rt_runtime_us 800000
write /dev/cpuctl/cpu.rt_period_us 1000000
mkdir /dev/cpuctl/bg_non_interactive
chown system system /dev/cpuctl/bg_non_interactive/tasks
chmod 0666 /dev/cpuctl/bg_non_interactive/tasks
# 5.0 %
write /dev/cpuctl/bg_non_interactive/cpu.shares 52
write /dev/cpuctl/bg_non_interactive/cpu.rt_runtime_us 700000
write /dev/cpuctl/bg_non_interactive/cpu.rt_period_us 1000000
In Documentation/scheduler/sched-rt-group.txt, cpu.rt_runtime_us is described as following:
2.3 Basis for grouping tasks
----------------------------
Enabling CONFIG_RT_GROUP_SCHED lets you explicitly allocate real
CPU bandwidth to task groups.
This uses the cgroup virtual file system and "<cgroup>/cpu.rt_runtime_us"
to control the CPU time reserved for each control group.
For more information on working with control groups, you should read
Documentation/cgroups/cgroups.txt as well.
Group settings are checked against the following limits in order to keep the
configuration schedulable:
\Sum_{i} runtime_{i} / global_period <= global_runtime / global_period
For now, this can be simplified to just the following (but see Future plans):
\Sum_{i} runtime_{i} <= global_runtime
In Documentation/scheduler/sched-rt-group.txt, cpu.rt_period_us is described as following:
3. Future plans
===============
There is work in progress to make the scheduling period for each group
("<cgroup>/cpu.rt_period_us") configurable as well.
The constraint on the period is that a subgroup must have a smaller or
equal period to its parent. But realistically its not very useful _yet_
as its prone to starvation without deadline scheduling.
Consider two sibling groups A and B; both have 50% bandwidth, but A's
period is twice the length of B's.
* group A: period=100000us, runtime=10000us
- this runs for 0.01s once every 0.1s
* group B: period= 50000us, runtime=10000us
- this runs for 0.01s twice every 0.1s (or once every 0.05 sec).
This means that currently a while (1) loop in A will run for the full period of
B and can starve B's tasks (assuming they are of lower priority) for a whole
period.
In Documentation/scheduler/sched-design-CFS.txt, cpu.shares is described as following:
When CONFIG_FAIR_GROUP_SCHED is defined, a "cpu.shares" file is created for each
group created using the pseudo filesystem. See example steps below to create
task groups and modify their CPU share using the "cgroups" pseudo filesystem.
# mount -t tmpfs cgroup_root /sys/fs/cgroup
# mkdir /sys/fs/cgroup/cpu
# mount -t cgroup -ocpu none /sys/fs/cgroup/cpu
# cd /sys/fs/cgroup/cpu
# mkdir multimedia # create "multimedia" group of tasks
# mkdir browser # create "browser" group of tasks
# #Configure the multimedia group to receive twice the CPU bandwidth
# #that of browser group
# echo 2048 > multimedia/cpu.shares
# echo 1024 > browser/cpu.shares
# firefox & # Launch firefox and move it to "browser" group
# echo <firefox_pid> > browser/tasks
# #Launch gmplayer (or your favourite movie player)
# echo <movie_player_pid> > multimedia/tasks
In system/core/libcutils/sched_policy.c:
int set_sched_policy(int tid, SchedPolicy policy)
{
if (tid == 0) {
tid = gettid();
}
policy = _policy(policy);
pthread_once(&the_once, __initialize);
.....
if (__sys_supports_schedgroups) {
int fd;
switch (policy) {
case SP_BACKGROUND:
fd = bg_cgroup_fd;
break;
case SP_FOREGROUND:
case SP_AUDIO_APP:
case SP_AUDIO_SYS:
fd = fg_cgroup_fd;
break;
default:
fd = -1;
break;
}
if (add_tid_to_cgroup(tid, fd) != 0) {
if (errno != ESRCH && errno != ENOENT) return -errno;
}
} else {
struct sched_param param;
param.sched_priority = 0;
sched_setscheduler(tid, (policy == SP_BACKGROUND) ? SCHED_BATCH : SCHED_NORMAL, ¶m);
}
prctl(PR_SET_TIMERSLACK_PID, policy == SP_BACKGROUND ? TIMER_SLACK_BG : TIMER_SLACK_FG, tid);
return 0;
}
SP_BACKGROUND will be set to the background group,
and the SP_FOREGROUND/SP_AUDIO_APP/SP_AUDIO_SYS will be set to foreground group
And set_sched_policy is only used in set_cpuset_policy when ENABLE_CPUSETS is set:
int set_cpuset_policy(int tid, SchedPolicy policy)
{
// in the absence of cpusets, use the old sched policy
#ifndef USE_CPUSETS
return set_sched_policy(tid, policy);
#else
....
}
Following are the places where set_sched_policy is called:
12:03:08 liuyq: marshmallow$ grep -rn set_sched_policy system/
system/bt/utils/src/bt_utils.c:127: // set_sched_policy does not support tid == 0
system/bt/utils/src/bt_utils.c:128: rc = set_sched_policy(tid, SP_AUDIO_SYS);
system/core/logd/main.cpp:90: if (set_sched_policy(0, SP_BACKGROUND) < 0) {
system/core/logd/main.cpp:170: set_sched_policy(0, SP_BACKGROUND);
system/core/include/cutils/sched_policy.h:29: SP_SYSTEM = 2, // can't be used with set_sched_policy()
system/core/include/cutils/sched_policy.h:45:extern int set_sched_policy(int tid, SchedPolicy policy);
system/core/logcat/logcat.cpp:216: if (set_sched_policy(0, SP_BACKGROUND) < 0) {
system/core/libutils/Threads.cpp:89: set_sched_policy(0, SP_BACKGROUND);
system/core/libutils/Threads.cpp:91: set_sched_policy(0, SP_FOREGROUND);
Called in androidCreateThreadEtc, androidCreateRawThreadEtc when Thread initialized with canCallJava
system/core/libutils/Threads.cpp:313: rc = set_sched_policy(tid, SP_BACKGROUND);
system/core/libutils/Threads.cpp:315: rc = set_sched_policy(tid, SP_FOREGROUND);
Called in functions in androidSetThreadPriority
called by android_os_Process_setThreadPriority in frameworks/base/core/jni/android_util_Process.cpp
others are called by media projects
system/core/libcutils/sched_policy.c:245: return set_sched_policy(tid, policy);
system/core/libcutils/sched_policy.c:277:int set_sched_policy(int tid, SchedPolicy policy)
system/core/libcutils/sched_policy.c:367:int set_sched_policy(int tid UNUSED, SchedPolicy policy UNUSED)
12:03:13 liuyq: marshmallow$ grep -rn set_sched_policy frameworks/
frameworks/av/media/libmedia/AudioTrack.cpp:581: set_sched_policy(0, mPreviousSchedulingGroup);
frameworks/av/media/libmedia/AudioTrack.cpp:621: set_sched_policy(0, mPreviousSchedulingGroup);
frameworks/av/media/libmedia/AudioRecord.cpp:359: set_sched_policy(0, mPreviousSchedulingGroup);
frameworks/av/media/libmedia/IMediaMetadataRetriever.cpp:54: set_sched_policy(gettid(), policy);
frameworks/av/media/libmedia/IMediaMetadataRetriever.cpp:58: set_sched_policy(gettid(), SP_FOREGROUND);
frameworks/base/core/jni/com_android_internal_os_Zygote.cpp:259: errno = -set_sched_policy(0, SP_DEFAULT);
frameworks/base/core/jni/com_android_internal_os_Zygote.cpp:261: ALOGE("set_sched_policy(0, SP_DEFAULT) failed");
frameworks/base/core/jni/android_util_Process.cpp:170: int res = set_sched_policy(tid, sp);
frameworks/base/core/jni/android_util_Process.cpp:272: err = set_sched_policy(t_pid, sp);
frameworks/native/libs/binder/IPCThreadState.cpp:447: set_sched_policy(mMyThreadId, SP_FOREGROUND);
frameworks/native/libs/binder/IPCThreadState.cpp:486: set_sched_policy(mMyThreadId, SP_FOREGROUND);
frameworks/native/libs/binder/IPCThreadState.cpp:1066: set_sched_policy(mMyThreadId, SP_BACKGROUND);
frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp:42: set_sched_policy(0, SP_FOREGROUND);
frameworks/native/cmds/installd/commands.cpp:1086: if (set_sched_policy(0, SP_BACKGROUND) < 0) {
frameworks/native/cmds/installd/commands.cpp:1087: ALOGE("set_sched_policy failed: %s\n", strerror(errno));
12:04:01 liuyq: marshmallow$
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