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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Thu, 12 Oct 2023 14:19:55 -0700
Message-ID: <CAJD7tkY9LrWHX3rjYwNnVK9sjtYPJyx6j_Y3DexTXfS9wwr+xA@mail.gmail.com>
Subject: Re: [PATCH v2 3/5] mm: memcg: make stats flushing threshold per-memcg
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Muchun Song <muchun.song@linux.dev>,
        Ivan Babrou <ivan@cloudflare.com>, Tejun Heo <tj@kernel.org>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        Waiman Long <longman@redhat.com>, kernel-team@cloudflare.com,
        Wei Xu <weixugc@google.com>, Greg Thelen <gthelen@google.com>,
        linux-mm@kvack.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Thu, Oct 12, 2023 at 2:16=E2=80=AFPM Shakeel Butt <shakeelb@google.com> =
wrote:
>
> On Thu, Oct 12, 2023 at 2:06=E2=80=AFPM Yosry Ahmed <yosryahmed@google.co=
m> wrote:
> >
> > [..]
> > > > > >
> > > > > > Using next-20231009 and a similar 44 core machine with hyperthr=
eading
> > > > > > 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 re=
duce
> > > > > > the noise? I am not sure.
> > > > > >
> > > > > > Please also keep in mind that in this case all netperf instance=
s are
> > > > > > in the same cgroup and at a 4-level depth. I imagine in a pract=
ical
> > > > > > setup processes would be a little more spread out, which means =
less
> > > > > > common ancestors, so less contended atomic operations.
> > > > >
> > > > >
> > > > > (Resending the reply as I messed up the last one, was not in plai=
n text)
> > > > >
> > > > > I was curious, so I ran the same testing in a cgroup 2 levels dee=
p
> > > > > (i.e /sys/fs/cgroup/a/b), which is a much more common setup in my
> > > > > experience. Here are the numbers:
> > > > >
> > > > > Base: 40198.0 mbps
> > > > > Patched: 38629.7 mbps
> > > > >
> > > > > The regression is reduced to ~3.9%.
> > > > >
> > > > > What's more interesting is that going from a level 2 cgroup to a =
level
> > > > > 4 cgroup is already a big hit with or without this patch:
> > > > >
> > > > > Base: 40198.0 -> 33076.5 mbps (~17.7% regression)
> > > > > Patched: 38629.7 -> 31410.1 (~18.7% regression)
> > > > >
> > > > > So going from level 2 to 4 is already a significant regression fo=
r
> > > > > other reasons (e.g. hierarchical charging). This patch only makes=
 it
> > > > > marginally worse. This puts the numbers more into perspective imo=
 than
> > > > > comparing values at level 4. What do you think?
> > > >
> > > > This is weird as we are running the experiments on the same machine=
. I
> > > > will rerun with 2 levels as well. Also can you rerun the page fault
> > > > benchmark as well which was showing 9% regression in your original
> > > > commit message?
> > >
> > > Thanks. I will re-run the page_fault tests, but keep in mind that the
> > > page fault benchmarks in will-it-scale are highly variable. We run
> > > them between kernel versions internally, and I think we ignore any
> > > changes below 10% as the benchmark is naturally noisy.
> > >
> > > I have a couple of runs for page_fault3_scalability showing a 2-3%
> > > improvement with this patch :)
> >
> > I ran the page_fault tests for 10 runs on a machine with 256 cpus in a
> > level 2 cgroup, here are the results (the results in the original
> > commit message are for 384 cpus in a level 4 cgroup):
> >
> >                LABEL            |     MEAN    |   MEDIAN    |   STDDEV =
  |
> > ------------------------------+-------------+-------------+------------=
-
> >   page_fault1_per_process_ops |             |             |            =
|
> >   (A) base                    | 270249.164  | 265437.000  | 13451.836  =
|
> >   (B) patched                 | 261368.709  | 255725.000  | 13394.767  =
|
> >                               | -3.29%      | -3.66%      |            =
|
> >   page_fault1_per_thread_ops  |             |             |            =
|
> >   (A) base                    | 242111.345  | 239737.000  | 10026.031  =
|
> >   (B) patched                 | 237057.109  | 235305.000  | 9769.687   =
|
> >                               | -2.09%      | -1.85%      |            =
|
> >   page_fault1_scalability     |             |             |
> >   (A) base                    | 0.034387    | 0.035168    | 0.0018283  =
|
> >   (B) patched                 | 0.033988    | 0.034573    | 0.0018056  =
|
> >                               | -1.16%      | -1.69%      |            =
|
> >   page_fault2_per_process_ops |             |             |
> >   (A) base                    | 203561.836  | 203301.000  | 2550.764   =
|
> >   (B) patched                 | 197195.945  | 197746.000  | 2264.263   =
|
> >                               | -3.13%      | -2.73%      |            =
|
> >   page_fault2_per_thread_ops  |             |             |
> >   (A) base                    | 171046.473  | 170776.000  | 1509.679   =
|
> >   (B) patched                 | 166626.327  | 166406.000  | 768.753    =
|
> >                               | -2.58%      | -2.56%      |            =
|
> >   page_fault2_scalability     |             |             |
> >   (A) base                    | 0.054026    | 0.053821    | 0.00062121 =
|
> >   (B) patched                 | 0.053329    | 0.05306     | 0.00048394 =
|
> >                               | -1.29%      | -1.41%      |            =
|
> >   page_fault3_per_process_ops |             |             |
> >   (A) base                    | 1295807.782 | 1297550.000 | 5907.585   =
|
> >   (B) patched                 | 1275579.873 | 1273359.000 | 8759.160   =
|
> >                               | -1.56%      | -1.86%      |            =
|
> >   page_fault3_per_thread_ops  |             |             |
> >   (A) base                    | 391234.164  | 390860.000  | 1760.720   =
|
> >   (B) patched                 | 377231.273  | 376369.000  | 1874.971   =
|
> >                               | -3.58%      | -3.71%      |            =
|
> >   page_fault3_scalability     |             |             |
> >   (A) base                    | 0.60369     | 0.60072     | 0.0083029  =
|
> >   (B) patched                 | 0.61733     | 0.61544     | 0.009855   =
|
> >                               | +2.26%      | +2.45%      |            =
|
> >
> > The numbers are much better. I can modify the commit log to include
> > the testing in the replies instead of what's currently there if this
> > helps (22 netperf instances on 44 cpus and will-it-scale page_fault on
> > 256 cpus -- all in a level 2 cgroup).
>
> Yes this looks better. I think we should also ask intel perf and
> phoronix folks to run their benchmarks as well (but no need to block
> on them).

Anything I need to do for this to happen? (I thought such testing is
already done on linux-next)

Also, any further comments on the patch (or the series in general)? If
not, I can send a new commit message for this patch in-place.