linux-kernel - Re: [PATCH v2 3/5] mm: memcg: make stats flushing threshold per-memcg

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Message-ID: <CAJD7tkbHWW139-=3HQM1cNzJGje9OYSCsDtNKKVmiNzRjE4tjQ@mail.gmail.com>
Date:   Wed, 11 Oct 2023 20:13:55 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        Ivan Babrou <ivan@...udflare.com>, Tejun Heo <tj@...nel.org>,
        Michal Koutný <mkoutny@...e.com>,
        Waiman Long <longman@...hat.com>, kernel-team@...udflare.com,
        Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] mm: memcg: make stats flushing threshold per-memcg

On Wed, Oct 11, 2023 at 5:46 AM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> On Tue, Oct 10, 2023 at 6:48 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> >
> > On Tue, Oct 10, 2023 at 5:36 PM Shakeel Butt <shakeelb@...gle.com> wrote:
> > >
> > > On Tue, Oct 10, 2023 at 03:21:47PM -0700, Yosry Ahmed wrote:
> > > [...]
> > > >
> > > > I tried this on a machine with 72 cpus (also ixion), running both
> > > > netserver and netperf in /sys/fs/cgroup/a/b/c/d as follows:
> > > > # echo "+memory" > /sys/fs/cgroup/cgroup.subtree_control
> > > > # mkdir /sys/fs/cgroup/a
> > > > # echo "+memory" > /sys/fs/cgroup/a/cgroup.subtree_control
> > > > # mkdir /sys/fs/cgroup/a/b
> > > > # echo "+memory" > /sys/fs/cgroup/a/b/cgroup.subtree_control
> > > > # mkdir /sys/fs/cgroup/a/b/c
> > > > # echo "+memory" > /sys/fs/cgroup/a/b/c/cgroup.subtree_control
> > > > # mkdir /sys/fs/cgroup/a/b/c/d
> > > > # echo 0 > /sys/fs/cgroup/a/b/c/d/cgroup.procs
> > > > # ./netserver -6
> > > >
> > > > # echo 0 > /sys/fs/cgroup/a/b/c/d/cgroup.procs
> > > > # for i in $(seq 10); do ./netperf -6 -H ::1 -l 60 -t TCP_SENDFILE --
> > > > -m 10K; done
> > >
> > > You are missing '&' at the end. Use something like below:
> > >
> > > #!/bin/bash
> > > for i in {1..22}
> > > do
> > >    /data/tmp/netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K &
> > > done
> > > wait
> > >
> >
> > Oh sorry I missed the fact that you are running instances in parallel, my bad.
> >
> > So I ran 36 instances on a machine with 72 cpus. I did this 10 times
> > and got an average from all instances for all runs to reduce noise:
> >
> > #!/bin/bash
> >
> > ITER=10
> > NR_INSTANCES=36
> >
> > for i in $(seq $ITER); do
> >   echo "iteration $i"
> >   for j in $(seq $NR_INSTANCES); do
> >     echo "iteration $i" >> "out$j"
> >     ./netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K >> "out$j" &
> >   done
> >   wait
> > done
> >
> > cat out* | grep 540000 | awk '{sum += $5} END {print sum/NR}'
> >
> > Base: 22169 mbps
> > Patched: 21331.9 mbps
> >
> > The difference is ~3.7% in my runs. I am not sure what's different.
> > Perhaps it's the number of runs?
>
> My base kernel is next-20231009 and I am running experiments with
> hyperthreading disabled.

Using next-20231009 and a similar 44 core machine with hyperthreading
disabled, I ran 22 instances of netperf in parallel and got the
following numbers from averaging 20 runs:

Base: 33076.5 mbps
Patched: 31410.1 mbps

That's about 5% diff. I guess the number of iterations helps reduce
the noise? I am not sure.

Please also keep in mind that in this case all netperf instances are
in the same cgroup and at a 4-level depth. I imagine in a practical
setup processes would be a little more spread out, which means less
common ancestors, so less contended atomic operations.