linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
* [PATCH 0/2] sched: Optionally skip uclamp logic in fast path
@ 2020-06-18 19:55 Qais Yousef
  2020-06-18 19:55 ` [PATCH 1/2] sched/uclamp: Fix initialization of strut uclamp_rq Qais Yousef
                   ` (2 more replies)
  0 siblings, 3 replies; 26+ messages in thread
From: Qais Yousef @ 2020-06-18 19:55 UTC (permalink / raw)
  To: Ingo Molnar, Peter Zijlstra
  Cc: Qais Yousef, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
	Steven Rostedt, Ben Segall, Mel Gorman, Patrick Bellasi,
	Chris Redpath, Lukasz Luba, linux-kernel

This series attempts to address the report that uclamp logic could be expensive
sometimes and shows a regression in netperf UDP_STREAM under certain
conditions.

The first patch is a fix for how struct uclamp_rq is initialized which is
required by the 2nd patch which contains the real 'fix'.

Worth noting that the root cause of the overhead is believed to be system
specific or related to potential certain code/data layout issues, leading to
worse I/D $ performance.

Different systems exhibited different behaviors and the regression did
disappear in certain kernel version while attempting to reporoduce.

More info can be found here:

https://lore.kernel.org/lkml/20200616110824.dgkkbyapn3io6wik@e107158-lin/

Having the static key seemed the best thing to do to ensure the effect of
uclamp is minimized for kernels that compile it in but don't have a userspace
that uses it, which will allow distros to distribute uclamp capable kernels by
default without having to compromise on performance for some systems that could
be affected.

Thanks

--
Qais Yousef

Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
CC: Patrick Bellasi <patrick.bellasi@matbug.net>
Cc: Chris Redpath <chrid.redpath@arm.com>
Cc: Lukasz Luba <lukasz.luba@arm.com>
Cc: linux-kernel@vger.kernel.org

Qais Yousef (2):
  sched/uclamp: Fix initialization of strut uclamp_rq
  sched/uclamp: Protect uclamp fast path code with static key

 kernel/sched/core.c | 73 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 64 insertions(+), 9 deletions(-)

-- 
2.17.1


^ permalink raw reply	[flat|nested] 26+ messages in thread

end of thread, other threads:[~2020-06-22 10:30 UTC | newest]

Thread overview: 26+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-06-18 19:55 [PATCH 0/2] sched: Optionally skip uclamp logic in fast path Qais Yousef
2020-06-18 19:55 ` [PATCH 1/2] sched/uclamp: Fix initialization of strut uclamp_rq Qais Yousef
2020-06-19 10:36   ` Valentin Schneider
2020-06-19 17:30   ` Peter Zijlstra
2020-06-19 17:39     ` Qais Yousef
2020-06-19 18:13       ` Peter Zijlstra
2020-06-19 18:42         ` Qais Yousef
2020-06-22 10:30           ` Qais Yousef
2020-06-18 19:55 ` [PATCH 2/2] sched/uclamp: Protect uclamp fast path code with static key Qais Yousef
2020-06-19 10:36   ` Valentin Schneider
2020-06-19 11:57     ` Mel Gorman
2020-06-19 12:17       ` Valentin Schneider
2020-06-19 12:55       ` Qais Yousef
2020-06-19 14:51       ` Qais Yousef
2020-06-19 12:51     ` Qais Yousef
2020-06-19 13:23       ` Steven Rostedt
2020-06-19 13:25       ` Valentin Schneider
2020-06-19 14:13         ` Qais Yousef
2020-06-19 15:17           ` Valentin Schneider
2020-06-19 17:25             ` Qais Yousef
2020-06-19 18:52               ` Valentin Schneider
2020-06-19 19:47         ` Peter Zijlstra
2020-06-19 10:39   ` Valentin Schneider
2020-06-19 17:45   ` Peter Zijlstra
2020-06-19 17:53     ` Qais Yousef
2020-06-22  9:06 ` [PATCH 0/2] sched: Optionally skip uclamp logic in fast path Lukasz Luba

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).