diff options
| author | Luis Chamberlain <mcgrof@kernel.org> | 2020-05-26 10:37:48 +1000 |
|---|---|---|
| committer | Stephen Rothwell <sfr@canb.auug.org.au> | 2020-05-28 19:43:30 +1000 |
| commit | 9183b884daa06948aed9148255c7622207df30ea (patch) | |
| tree | 37b87ec9e6fd7c3731a7f13b2b6e788032b6e924 | |
| parent | 51fb4b94da66f5fb62723514e6457ff187dc0447 (diff) | |
include/linux/cache.h: expand documentation over __read_mostly
__read_mostly can easily be misused by folks, its not meant for just
read-only data. There are performance reasons for using it, but we also
don't provide any guidance about its use. Provide a bit more guidance
over its use.
Link: http://lkml.kernel.org/r/20200507161424.2584-1-mcgrof@kernel.org
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Christoph Lameter <cl@linux.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Rafael Aquini <aquini@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
| -rw-r--r-- | include/linux/cache.h | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/include/linux/cache.h b/include/linux/cache.h index 750621e41d1c..1aa8009f6d06 100644 --- a/include/linux/cache.h +++ b/include/linux/cache.h @@ -15,8 +15,14 @@ /* * __read_mostly is used to keep rarely changing variables out of frequently - * updated cachelines. If an architecture doesn't support it, ignore the - * hint. + * updated cachelines. Its use should be reserved for data that is used + * frequently in hot paths. Performance traces can help decide when to use + * this. You want __read_mostly data to be tightly packed, so that in the + * best case multiple frequently read variables for a hot path will be next + * to each other in order to reduce the number of cachelines needed to + * execute a critical path. We should be mindful and selective of its use. + * ie: if you're going to use it please supply a *good* justification in your + * commit log */ #ifndef __read_mostly #define __read_mostly |