From: Mel Gorman <mgorman@techsingularity.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: kernel test robot <oliver.sang@intel.com>,
Sandeep Patil <sspatil@android.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
lkp@lists.01.org, kernel test robot <lkp@intel.com>,
"Huang, Ying" <ying.huang@intel.com>,
Feng Tang <feng.tang@intel.com>,
Zhengjun Xing <zhengjun.xing@linux.intel.com>
Subject: Re: [pipe] 3a34b13a88: hackbench.throughput -12.6% regression
Date: Wed, 18 Aug 2021 16:31:55 +0100 [thread overview]
Message-ID: <20210818153155.GL6464@techsingularity.net> (raw)
In-Reply-To: <CAHk-=whYu7f=itjJJTfAWdDN2Baz0whdU1bzxh_5RAfj+LyB3g@mail.gmail.com>
On Mon, Aug 02, 2021 at 10:14:14AM -0700, Linus Torvalds wrote:
> On Mon, Aug 2, 2021 at 10:06 AM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Sandeep, does something like the attached patch (written to be on top
> > of the existing one) work for you?
>
> .. and by "attached patch" I obviously meant the patch that wasn't attached.
>
> It's here.
>
Hi Linus,
Our own test systems also detected the regression and automatically
bisected to 3a34b13a88 but it is not universal. For example, it's not
visible on a single socket 8-cpu skylake machine but it gets progressively
worse the more CPUs there are and potentially the more LLCs there are. I
say LLCs because the number of interrupts generated was significantly
higher which *might* be more IPIs being sent to tasks running on CPUs
that do not share target with the waker.
Your "attached" patch alleviates the problem. The worse results were on
a Zen3 machine (256 CPUs, lots of last level caches).
hackbench-process-pipes
5.14.0-rc3 5.14.0-rc3 5.14.0-rc3
vanilla alwayswake-v1r1 specialcase-v1r1
Amean 1 0.3800 ( 0.00%) 0.4520 * -18.95%* 0.3580 ( 5.79%)
Amean 4 0.5107 ( 0.00%) 0.6660 * -30.42%* 0.5080 ( 0.52%)
Amean 7 0.5717 ( 0.00%) 0.6387 * -11.72%* 0.5310 * 7.11%*
Amean 12 0.5853 ( 0.00%) 0.8563 * -46.30%* 0.5457 ( 6.78%)
Amean 21 0.7693 ( 0.00%) 1.3150 * -70.93%* 0.7297 ( 5.16%)
Amean 30 0.9667 ( 0.00%) 1.8530 * -91.69%* 0.8547 ( 11.59%)
Amean 48 1.3100 ( 0.00%) 2.5027 * -91.04%* 1.3143 ( -0.33%)
Amean 79 2.0633 ( 0.00%) 3.4983 * -69.55%* 2.1180 ( -2.65%)
Amean 110 2.8080 ( 0.00%) 3.9927 * -42.19%* 2.7850 ( 0.82%)
Amean 141 3.6237 ( 0.00%) 4.6810 * -29.18%* 3.6663 ( -1.18%)
Amean 172 4.6480 ( 0.00%) 5.6707 * -22.00%* 4.8003 ( -3.28%)
Amean 203 5.2630 ( 0.00%) 6.5000 * -23.50%* 5.6100 ( -6.59%)
Amean 234 6.3290 ( 0.00%) 7.1473 * -12.93%* 6.1570 ( 2.72%)
Amean 265 7.0907 ( 0.00%) 7.9200 * -11.70%* 7.1417 ( -0.72%)
Amean 296 7.7550 ( 0.00%) 8.2590 * -6.50%* 7.8167 ( -0.80%)
alwayswake-v1r1 is commit 3a34b13a88 cherry-picked on top of 5.14-rc3.
specialcase-v1r1 is your suggested patch on top.
The * mark results that are likely statistically significant so with
your suggested patch, most of the results are mostly in the noise.
While this is Zen3, the same problem exists on at least 2-socket
cascadelake, 2-socket skylake and 2-socket broadwell systems although
not to the same degree (different CPU counts and topology).
I know hackbench is not particularly interesting but it's used often
enough when comparing kernels and patches that commit 3a34b13a88 will be
a regression magnet.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2021-08-18 15:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-02 2:49 [pipe] 3a34b13a88: hackbench.throughput -12.6% regression kernel test robot
2021-08-02 17:06 ` Linus Torvalds
2021-08-02 17:14 ` Linus Torvalds
2021-08-10 18:24 ` Sandeep Patil
2021-08-18 15:31 ` Mel Gorman [this message]
2021-08-18 18:17 ` Linus Torvalds
2021-08-11 15:46 ` Sandeep Patil
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