From: Mel Gorman <mgorman@techsingularity.net>
To: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Aubrey Li <aubrey.li@linux.intel.com>,
Barry Song <song.bao.hua@hisilicon.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] sched/fair: Couple wakee flips with heavy wakers
Date: Fri, 22 Oct 2021 12:05:34 +0100 [thread overview]
Message-ID: <20211022110534.GJ3959@techsingularity.net> (raw)
In-Reply-To: <37d8c167df66a1ead16b699115548ca376494c0c.camel@gmx.de>
On Fri, Oct 22, 2021 at 12:26:08PM +0200, Mike Galbraith wrote:
> On Thu, 2021-10-21 at 15:56 +0100, Mel Gorman wrote:
> >
> > From additional tests on various servers, the impact is machine dependant
> > but generally this patch improves the situation.
> >
> > hackbench-process-pipes
> > 5.15.0-rc3 5.15.0-rc3
> > vanilla sched-wakeeflips-v1r1
> > Amean 1 0.3667 ( 0.00%) 0.3890 ( -6.09%)
> > Amean 4 0.5343 ( 0.00%) 0.5217 ( 2.37%)
> > Amean 7 0.5300 ( 0.00%) 0.5387 ( -1.64%)
> > Amean 12 0.5737 ( 0.00%) 0.5443 ( 5.11%)
> > Amean 21 0.6727 ( 0.00%) 0.6487 ( 3.57%)
> > Amean 30 0.8583 ( 0.00%) 0.8033 ( 6.41%)
> > Amean 48 1.3977 ( 0.00%) 1.2400 * 11.28%*
> > Amean 79 1.9790 ( 0.00%) 1.8200 * 8.03%*
> > Amean 110 2.8020 ( 0.00%) 2.5820 * 7.85%*
> > Amean 141 3.6683 ( 0.00%) 3.2203 * 12.21%*
> > Amean 172 4.6687 ( 0.00%) 3.8200 * 18.18%*
> > Amean 203 5.2183 ( 0.00%) 4.3357 * 16.91%*
> > Amean 234 6.1077 ( 0.00%) 4.8047 * 21.33%*
> > Amean 265 7.1313 ( 0.00%) 5.1243 * 28.14%*
> > Amean 296 7.7557 ( 0.00%) 5.5940 * 27.87%*
> >
> > While different machines showed different results, in general
> > there were much less CPU migrations of tasks
>
> Patchlet helped hackbench? That's.. unexpected (at least by me).
>
I didn't analyse in depth and other machines do not show as dramatic
a difference but it's likely due to timings of tasks getting wakeup
preempted. On a 2-socket cascadelake machine the difference was -7.4%
to 7.66% depending on group count. The second biggest loss was -0.71%
and more gains than losses. In each case, CPU migrations and system CPU
usage are reduced.
The big difference here is likely because the machine is Zen 3 and has
multiple LLCs per cache so it suffers more if there are imbalances between
LLCs that wouldn't be visible on most Intel machines with 1 LLC per socket.
> > tbench4
> > 5.15.0-rc3 5.15.0-rc3
> > vanilla sched-wakeeflips-v1r1
> > Hmean 1 824.05 ( 0.00%) 802.56 * -2.61%*
> > Hmean 2 1578.49 ( 0.00%) 1645.11 * 4.22%*
> > Hmean 4 2959.08 ( 0.00%) 2984.75 * 0.87%*
> > Hmean 8 5080.09 ( 0.00%) 5173.35 * 1.84%*
> > Hmean 16 8276.02 ( 0.00%) 9327.17 * 12.70%*
> > Hmean 32 15501.61 ( 0.00%) 15925.55 * 2.73%*
> > Hmean 64 27313.67 ( 0.00%) 24107.81 * -11.74%*
> > Hmean 128 32928.19 ( 0.00%) 36261.75 * 10.12%*
> > Hmean 256 35434.73 ( 0.00%) 38670.61 * 9.13%*
> > Hmean 512 50098.34 ( 0.00%) 53243.75 * 6.28%*
> > Hmean 1024 69503.69 ( 0.00%) 67425.26 * -2.99%*
> >
> > Bit of a mixed bag but wins more than it loses.
>
> Hm. If patchlet repeatably impacts buddy pairs one way or the other,
> it should probably be tossed out the nearest window.
>
I don't see how buddy pairing would be impacted although there is likely
differences in the degree tasks get preempted due to pulling tasks.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2021-10-22 11:05 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-21 14:56 [PATCH 0/2] Reduce stacking and overscheduling Mel Gorman
2021-10-21 14:56 ` [PATCH 1/2] sched/fair: Couple wakee flips with heavy wakers Mel Gorman
2021-10-22 10:26 ` Mike Galbraith
2021-10-22 11:05 ` Mel Gorman [this message]
2021-10-22 12:00 ` Mike Galbraith
2021-10-25 6:35 ` Mike Galbraith
2021-10-26 8:18 ` Mel Gorman
2021-10-26 10:15 ` Mike Galbraith
2021-10-26 10:41 ` Mike Galbraith
2021-10-26 11:57 ` Mel Gorman
2021-10-26 12:13 ` Mike Galbraith
2021-10-27 2:09 ` Mike Galbraith
2021-10-27 9:00 ` Mel Gorman
2021-10-27 10:18 ` Mike Galbraith
2021-11-09 11:56 ` Peter Zijlstra
2021-11-09 12:55 ` Mike Galbraith
2021-10-21 14:56 ` [PATCH 2/2] sched/fair: Increase wakeup_gran if current task has not executed the minimum granularity Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2021-10-28 9:48 [PATCH v4 0/2] Reduce stacking and overscheduling Mel Gorman
2021-10-28 9:48 ` [PATCH 1/2] sched/fair: Couple wakee flips with heavy wakers Mel Gorman
2021-10-28 16:19 ` Tao Zhou
2021-10-29 8:42 ` Mel Gorman
2021-11-10 9:53 ` Tao Zhou
2021-11-10 15:40 ` Mike Galbraith
2021-10-29 15:17 ` Vincent Guittot
2021-10-30 3:11 ` Mike Galbraith
2021-10-30 4:12 ` Mike Galbraith
2021-11-01 8:56 ` Mel Gorman
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