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From: Valentin Schneider <valentin.schneider@arm.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Qais Yousef <qais.yousef@arm.com>, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>,
	Patrick Bellasi <patrick.bellasi@matbug.net>,
	Chris Redpath <chrid.redpath@arm.com>,
	Lukasz Luba <lukasz.luba@arm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] sched/uclamp: Protect uclamp fast path code with static key
Date: Fri, 19 Jun 2020 13:17:28 +0100	[thread overview]
Message-ID: <jhjtuz7ckrr.mognet@arm.com> (raw)
In-Reply-To: <20200619115723.GF3129@suse.de>


On 19/06/20 12:57, Mel Gorman wrote:
> On Fri, Jun 19, 2020 at 11:36:46AM +0100, Valentin Schneider wrote:
>> >                                    nouclamp                 uclamp      uclamp-static-key
>> > Hmean     send-64         162.43 (   0.00%)      157.84 *  -2.82%*      163.39 *   0.59%*
>> > Hmean     send-128        324.71 (   0.00%)      314.78 *  -3.06%*      326.18 *   0.45%*
>> > Hmean     send-256        641.55 (   0.00%)      628.67 *  -2.01%*      648.12 *   1.02%*
>> > Hmean     send-1024      2525.28 (   0.00%)     2448.26 *  -3.05%*     2543.73 *   0.73%*
>> > Hmean     send-2048      4836.14 (   0.00%)     4712.08 *  -2.57%*     4867.69 *   0.65%*
>> > Hmean     send-3312      7540.83 (   0.00%)     7425.45 *  -1.53%*     7621.06 *   1.06%*
>> > Hmean     send-4096      9124.53 (   0.00%)     8948.82 *  -1.93%*     9276.25 *   1.66%*
>> > Hmean     send-8192     15589.67 (   0.00%)    15486.35 *  -0.66%*    15819.98 *   1.48%*
>> > Hmean     send-16384    26386.47 (   0.00%)    25752.25 *  -2.40%*    26773.74 *   1.47%*
>> >
>>
>> Am I reading this correctly in that compiling in uclamp but having the
>> static key enabled gives a slight improvement compared to not compiling in
>> uclamp? I suppose the important bit is that we're not seeing regressions
>> anymore, but still.
>>
>
> I haven't reviewed the series in depth because from your review, another
> version is likely in the works.

I don't wait Qais to hate me here - I think you could start the performance
testing on this version if you feel like it, given my comments were mostly
on changelog / debug options - the core of that patch shouldn't change
much.

> However, it is not that unusual to
> see small fluctuations like this that are counter-intuitive. The report
> indicates the difference is likely outside of the noise with * around the
> percentage difference instead of () but it could be small boot-to-boot
> variance, differences in code layout, slight differences in slab usage
> patterns etc. The definitive evidence that uclamp overhead is no there
> is whether the uclamp functions show up in annotated profiles or not.

I see, thanks! I suppose if we have access to individual samples we can
also run some statistical tests / stare at some boxplots to see how it
compares.

  reply	other threads:[~2020-06-19 12:17 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 [this message]
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

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