[RFC PATCH v2 2/2] scheduler: add scheduler level for clusters

Mon Dec 7 04:59:21 EST 2020

> -----Original Message-----
> From: Vincent Guittot [mailto:vincent.guittot at linaro.org]
> Sent: Thursday, December 3, 2020 10:39 PM
> To: Song Bao Hua (Barry Song) <song.bao.hua at hisilicon.com>
> Cc: Valentin Schneider <valentin.schneider at arm.com>; Catalin Marinas
> <catalin.marinas at arm.com>; Will Deacon <will at kernel.org>; Rafael J. Wysocki
> <rjw at rjwysocki.net>; Cc: Len Brown <lenb at kernel.org>;
> gregkh at linuxfoundation.org; Jonathan Cameron <jonathan.cameron at huawei.com>;
> Ingo Molnar <mingo at redhat.com>; Peter Zijlstra <peterz at infradead.org>; Juri
> Lelli <juri.lelli at redhat.com>; Dietmar Eggemann <dietmar.eggemann at arm.com>;
> Steven Rostedt <rostedt at goodmis.org>; Ben Segall <bsegall at google.com>; Mel
> Gorman <mgorman at suse.de>; Mark Rutland <mark.rutland at arm.com>; LAK
> <linux-arm-kernel at lists.infradead.org>; linux-kernel
> <linux-kernel at vger.kernel.org>; ACPI Devel Maling List
> <linux-acpi at vger.kernel.org>; Linuxarm <linuxarm at huawei.com>; xuwei (O)
> <xuwei5 at huawei.com>; Zengtao (B) <prime.zeng at hisilicon.com>
> Subject: Re: [RFC PATCH v2 2/2] scheduler: add scheduler level for clusters
> 
> On Thu, 3 Dec 2020 at 10:11, Song Bao Hua (Barry Song)
> <song.bao.hua at hisilicon.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Vincent Guittot [mailto:vincent.guittot at linaro.org]
> > > Sent: Thursday, December 3, 2020 10:04 PM
> > > To: Song Bao Hua (Barry Song) <song.bao.hua at hisilicon.com>
> > > Cc: Valentin Schneider <valentin.schneider at arm.com>; Catalin Marinas
> > > <catalin.marinas at arm.com>; Will Deacon <will at kernel.org>; Rafael J. Wysocki
> > > <rjw at rjwysocki.net>; Cc: Len Brown <lenb at kernel.org>;
> > > gregkh at linuxfoundation.org; Jonathan Cameron
> <jonathan.cameron at huawei.com>;
> > > Ingo Molnar <mingo at redhat.com>; Peter Zijlstra <peterz at infradead.org>; Juri
> > > Lelli <juri.lelli at redhat.com>; Dietmar Eggemann
> <dietmar.eggemann at arm.com>;
> > > Steven Rostedt <rostedt at goodmis.org>; Ben Segall <bsegall at google.com>; Mel
> > > Gorman <mgorman at suse.de>; Mark Rutland <mark.rutland at arm.com>; LAK
> > > <linux-arm-kernel at lists.infradead.org>; linux-kernel
> > > <linux-kernel at vger.kernel.org>; ACPI Devel Maling List
> > > <linux-acpi at vger.kernel.org>; Linuxarm <linuxarm at huawei.com>; xuwei (O)
> > > <xuwei5 at huawei.com>; Zengtao (B) <prime.zeng at hisilicon.com>
> > > Subject: Re: [RFC PATCH v2 2/2] scheduler: add scheduler level for clusters
> > >
> > > On Wed, 2 Dec 2020 at 21:58, Song Bao Hua (Barry Song)
> > > <song.bao.hua at hisilicon.com> wrote:
> > > >
> > > > >
> > > > > Sorry. Please ignore this. I added some printk here while testing
> > > > > one numa. Will update you the data in another email.
> > > >
> > > > Re-tested in one NUMA node(cpu0-cpu23):
> > > >
> > > > g=1
> > > > Running in threaded mode with 1 groups using 40 file descriptors
> > > > Each sender will pass 100000 messages of 100 bytes
> > > > w/o: 7.689 7.485 7.485 7.458 7.524 7.539 7.738 7.693 7.568 7.674=7.5853
> > > > w/ : 7.516 7.941 7.374 7.963 7.881 7.910 7.420 7.556 7.695 7.441=7.6697
> > > > w/ but dropped select_idle_cluster:
> > > >      7.752 7.739 7.739 7.571 7.545 7.685 7.407 7.580 7.605 7.487=7.611
> > > >
> > > > g=2
> > > > Running in threaded mode with 2 groups using 40 file descriptors
> > > > Each sender will pass 100000 messages of 100 bytes
> > > > w/o: 10.127 10.119 10.070 10.196 10.057 10.111 10.045 10.164 10.162
> > > > 9.955=10.1006
> > > > w/ : 9.694 9.654 9.612 9.649 9.686 9.734 9.607 9.842 9.690 9.710=9.6878
> > > > w/ but dropped select_idle_cluster:
> > > >      9.877 10.069 9.951 9.918 9.947 9.790 9.906 9.820 9.863 9.906=9.9047
> > > >
> > > > g=3
> > > > Running in threaded mode with 3 groups using 40 file descriptors
> > > > Each sender will pass 100000 messages of 100 bytes
> > > > w/o: 15.885 15.254 15.932 15.647 16.120 15.878 15.857 15.759 15.674
> > > > 15.721=15.7727
> > > > w/ : 14.974 14.657 13.969 14.985 14.728 15.665 15.191 14.995 14.946
> > > > 14.895=14.9005
> > > > w/ but dropped select_idle_cluster:
> > > >      15.405 15.177 15.373 15.187 15.450 15.540 15.278 15.628 15.228
> > > 15.325=15.3591
> > > >
> > > > g=4
> > > > Running in threaded mode with 4 groups using 40 file descriptors
> > > > Each sender will pass 100000 messages of 100 bytes
> > > > w/o: 20.014 21.025 21.119 21.235 19.767 20.971 20.962 20.914 21.090
> > > 21.090=20.8187
> > > > w/ : 20.331 20.608 20.338 20.445 20.456 20.146 20.693 20.797 21.381
> > > 20.452=20.5647
> > > > w/ but dropped select_idle_cluster:
> > > >      19.814 20.126 20.229 20.350 20.750 20.404 19.957 19.888 20.226
> > > 20.562=20.2306
> > > >
> > >
> > > I assume that you have run this on v5.9 as previous tests.
> >
> > Yep
> >
> > > The results don't show any real benefit of select_idle_cluster()
> > > inside a node whereas this is where we could expect most of the
> > > benefit. We have to understand why we have such an impact on numa
> > > tests only.
> >
> > There is a 4-5.5% increase while g=2 and g=3.
> 
> my point was with vs without select_idle_cluster() but still having a
> cluster domain level
> In this case, the diff is -0.8% for g=1 +2.2% for g=2, +3% for g=3 and
> -1.7% for g=4
> 
> >
> > Regarding the huge increase in NUMA case,  at the first beginning, I suspect
> > we have wrong llc domain. For example, if cpu0's llc domain span
> > cpu0-cpu47, then select_idle_cpu() is running in wrong range while
> > it should run in cpu0-cpu23.
> >
> > But after printing the llc domain's span, I find it is completely right.
> > Cpu0's llc span: cpu0-cpu23
> > Cpu24's llc span: cpu24-cpu47
> 
> Have you checked that the cluster mask was also correct ?
> 
> >
> > Maybe I need more trace data to figure out if select_idle_cpu() is running
> > correctly. For example, maybe I can figure out if it is always returning -1,
> > or it returns -1 very often?
> 
> yes, could be interesting to check how often select_idle_cpu return -1
> 
> >
> > Or do you have any idea?
> 
> tracking migration across nod could help to understand too

I set a bootargs mem=4G to do swapping test before working on cluster
scheduler issue. but I forgot to remove the parameter.

The huge increase on across-numa case can only be reproduced while
i use this mem=4G cmdline which means numa1 has no memory.
After removing the limitation, I can't reproduce the huge increase
for two NUMAs any more.

Guess select_idle_cluster() somehow workaround an scheduler issue
for numa without memory.

> 
> Vincent
> >
> >

Thanks
Barry