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Date: Thu, 25 Oct 2018 10:31:00 +0100
From: Patrick Bellasi <patrick.bellasi@....com>
To: Aaron Lu <aaron.lu@...el.com>
Cc: "Ye, Xiaolong" <xiaolong.ye@...el.com>,
Joel Fernandes <joelaf@...gle.com>,
Juri Lelli <juri.lelli@...hat.com>,
Todd Kjos <tkjos@...roid.com>,
Stephen Rothwell <sfr@...b.auug.org.au>,
Peter Zijlstra <peterz@...radead.org>,
Paul Turner <pjt@...gle.com>,
"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
Morten Rasmussen <morten.rasmussen@....com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steve Muckle <smuckle@...gle.com>, "lkp@...org" <lkp@...org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Chris Redpath <chris.redpath@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [LKP] [lkp-robot] [sched/fair] d519329f72: unixbench.score -9.9%
regression
On 25-Oct 16:56, Aaron Lu wrote:
> On Wed, Oct 24, 2018 at 06:01:37PM +0100, Patrick Bellasi wrote:
> > On 24-Oct 14:41, Aaron Lu wrote:
> > > On Mon, Apr 02, 2018 at 11:20:00AM +0800, Ye, Xiaolong wrote:
> > > >
> > > > Greeting,
> > > >
> > > > FYI, we noticed a -9.9% regression of unixbench.score due to commit:
> > > >
> > > >
> > > > commit: d519329f72a6f36bc4f2b85452640cfe583b4f81 ("sched/fair: Update util_est only on util_avg updates")
> > > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> > > >
> > > > in testcase: unixbench
> > > > on test machine: 8 threads Intel(R) Core(TM) i7 CPU 870 @ 2.93GHz with 6G memory
> > > > with following parameters:
> > > >
> > > > runtime: 300s
> > > > nr_task: 100%
> > > > test: execl
> > > >
> > > > test-description: UnixBench is the original BYTE UNIX benchmark suite aims to test performance of Unix-like system.
> > > > test-url: https://github.com/kdlucas/byte-unixbench
> >
> > Hi Aaron,
> >
> > > I tested this workload on different machines with this commit
> > > d519329f72a6f36bc4f2b85452 and its parent a07630b8b2c16f82, I also
> > > tested with v4.19-rc8 to see if the regression is gone -
> > > the performance drop is there with v4.19-rc8 and with different
> > > machines so I assume this regression is not solved yet.
> > >
> > > Here are detailed data:
> > >
> > > cmdline used to run this workload:
> > > ./Run execl -c $nr_cpu -i 30
> >
> > I had a better look into this issue and found that something like this
> > could be the cure for the execl throughput regression:
>
> Good news, yes they are!
Great.
> > ---8<---
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 908c9cdae2f0..c34d41b542fc 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6258,8 +6258,17 @@ static unsigned long cpu_util_wake(int cpu, struct task_struct *p)
> > * covered by the following code when estimated utilization is
> > * enabled.
> > */
> > - if (sched_feat(UTIL_EST))
> > - util = max(util, READ_ONCE(cfs_rq->avg.util_est.enqueued));
> > + if (sched_feat(UTIL_EST)) {
> > + unsigned int estimated =
> > + READ_ONCE(cfs_rq->avg.util_est.enqueued);
> > +
> > + if (unlikely(current == p)) {
> > + estimated -= min_t(unsigned int, estimated,
> > + (_task_util_est(p) | UTIL_AVG_UNCHANGED));
> > + }
> > +
> > + util = max(util, estimated);
> > + }
> >
> > /*
> > * Utilization (estimated) can exceed the CPU capacity, thus let's
> > ---8<---
> >
> > I'll test this better on a machine on my side and send out a proper
> > patch by tomorrow.
> >
> > > Please let me know if you need other information, thanks.
> >
> > Would be nice if you can test the above on your side too.
> >
>
> commit cbcb74a95c5af32f9127a102feca323139ba2c49 is the commit I made
> from your diff and it restored performance for the two desktops. the
> result on the skylake server isn't quite stable so I think the
> performance gap is due to noise.
>
> lkp-ivb-d04:
> cbcb74a95c5af32f9127a102feca323139ba2c49/avg.json: "unixbench.score": 2946.0,
> d519329f72a6f36bc4f2b85452640cfe583b4f81/avg.json: "unixbench.score": 2669.5333333333333,
> a07630b8b2c16f82fd5b71d890079f4dd7599c1d/avg.json: "unixbench.score": 2924.3333333333335,
>
> lkp-hsw-d01:
> cbcb74a95c5af32f9127a102feca323139ba2c49/avg.json: "unixbench.score": 7013.533333333333,
> d519329f72a6f36bc4f2b85452640cfe583b4f81/avg.json: "unixbench.score": 6421.233333333333,
> a07630b8b2c16f82fd5b71d890079f4dd7599c1d/avg.json: "unixbench.score": 7090.400000000001,
>
> lkp-skl-2sp2:
> cbcb74a95c5af32f9127a102feca323139ba2c49/avg.json: "unixbench.score": 9347.02,
> d519329f72a6f36bc4f2b85452640cfe583b4f81/avg.json: "unixbench.score": 9362.76,
> a07630b8b2c16f82fd5b71d890079f4dd7599c1d/avg.json: "unixbench.score": 9520.86,
I've measured a ~15% speedup with the patch in wrt v4.19.0 on a
40 CPUs Intel(R) Xeon(R) CPU E5-2690 v2 @ 3.00GHz.
################################################################################
### Mainline (v4.19.0):
Benchmark Run: Wed Oct 24 2018 16:13:34 - 16:19:04
40 CPUs in system; running 40 parallel copies of tests
Execl Throughput 48136.5 lps (29.9 s, 7 samples)
System Benchmarks Partial Index BASELINE RESULT INDEX
Execl Throughput 43.0 48136.5 11194.5
========
System Benchmarks Index Score (Partial Only) 11194.5
################################################################################
### Mainline (v4.19.0) + patch:
Benchmark Run: Wed Oct 24 2018 16:29:56 - 16:35:26
40 CPUs in system; running 40 parallel copies of tests
Execl Throughput 55373.6 lps (29.9 s, 7 samples)
System Benchmarks Partial Index BASELINE RESULT INDEX
Execl Throughput 43.0 55373.6 12877.6
========
System Benchmarks Index Score (Partial Only) 12877.6
################################################################################
Thanks again reporting and testing on your side, I'll post soon a proper
patch.
Cheers Patrick
--
#include <best/regards.h>
Patrick Bellasi
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