linux-kernel - Re: [PATCH v4 11/11] sched/fair: rework find_idlest

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Message-ID: <20191120181002.lh7vukjm2ifhysbc@e107158-lin.cambridge.arm.com>
Date:   Wed, 20 Nov 2019 18:10:02 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Hillf Danton <hdanton@...a.com>,
        Parth Shah <parth@...ux.ibm.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v4 11/11] sched/fair: rework find_idlest_group

On 11/20/19 18:43, Vincent Guittot wrote:
> On Wed, 20 Nov 2019 at 18:34, Qais Yousef <qais.yousef@....com> wrote:
> >
> > On 11/20/19 17:53, Vincent Guittot wrote:
> > > On Wed, 20 Nov 2019 at 14:21, Vincent Guittot
> > > <vincent.guittot@...aro.org> wrote:
> > > >
> > > > Hi Qais,
> > > >
> > > > On Wed, 20 Nov 2019 at 12:58, Qais Yousef <qais.yousef@....com> wrote:
> > > > >
> > > > > Hi Vincent
> > > > >
> > > > > On 10/18/19 15:26, Vincent Guittot wrote:
> > > > > > The slow wake up path computes per sched_group statisics to select the
> > > > > > idlest group, which is quite similar to what load_balance() is doing
> > > > > > for selecting busiest group. Rework find_idlest_group() to classify the
> > > > > > sched_group and select the idlest one following the same steps as
> > > > > > load_balance().
> > > > > >
> > > > > > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> > > > > > ---
> > > > >
> > > > > LTP test has caught a regression in perf_event_open02 test on linux-next and I
> > > > > bisected it to this patch.
> > > > >
> > > > > That is checking out next-20191119 tag and reverting this patch on top the test
> > > > > passes. Without the revert the test fails.
> > >
> > > I haven't tried linux-next yet but LTP test is passed with
> > > tip/sched/core, which includes this patch, on hikey960 which is arm64
> > > too.
> > >
> > > Have you tried tip/sched/core on your juno ? this could help to
> > > understand if it's only for juno or if this patch interact with
> > > another branch merged in linux next
> >
> > Okay will give it a go. But out of curiosity, what is the output of your run?
> >
> > While bisecting on linux-next I noticed that at some point the test was
> > passing but all the read values were 0. At some point I started seeing
> > none-zero values.
> 
> for tip/sched/core
> linaro@...aro-developer:~/ltp/testcases/kernel/syscalls/perf_event_open$
> sudo ./perf_event_open02
> perf_event_open02    0  TINFO  :  overall task clock: 63724479
> perf_event_open02    0  TINFO  :  hw sum: 1800900992, task clock sum: 382170311
> perf_event_open02    0  TINFO  :  ratio: 5.997229
> perf_event_open02    1  TPASS  :  test passed
> 
> for next-2019119
> ~/ltp/testcases/kernel/syscalls/perf_event_open$ sudo ./perf_event_open02 -v
> at iteration:0 value:0 time_enabled:69795312 time_running:0
> perf_event_open02    0  TINFO  :  overall task clock: 63582292
> perf_event_open02    0  TINFO  :  hw sum: 0, task clock sum: 0
> hw counters: 0 0 0 0
> task clock counters: 0 0 0 0
> perf_event_open02    0  TINFO  :  ratio: 0.000000
> perf_event_open02    1  TPASS  :  test passed

Okay that is weird. But ratio, hw sum, task clock sum are all 0 in your
next-20191119. I'm not sure why the counters return 0 sometimes - is it
dependent on some option or a bug somewhere.

I just did another run and it failed for me (building with defconfig)

# uname -a
Linux buildroot 5.4.0-rc8-next-20191119 #72 SMP PREEMPT Wed Nov 20 17:57:48 GMT 2019 aarch64 GNU/Linux

# ./perf_event_open02 -v
at iteration:0 value:260700250 time_enabled:172739760 time_running:144956600
perf_event_open02    0  TINFO  :  overall task clock: 166915220
perf_event_open02    0  TINFO  :  hw sum: 1200718268, task clock sum: 667621320
hw counters: 300179051 300179395 300179739 300180083
task clock counters: 166906620 166906200 166905160 166903340
perf_event_open02    0  TINFO  :  ratio: 3.999763
perf_event_open02    0  TINFO  :  nhw: 0.000100
perf_event_open02    1  TFAIL  :  perf_event_open02.c:370: test failed (ratio was greater than )

It is a funny one for sure. I haven't tried tip/sched/core yet.

Thanks

--
Qais Yousef