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

Shakeel Butt
2023-10-12T21:16:41Z

On Thu, Oct 12, 2023 at 2:06 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> [..]
> > > > >
> > > > > 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.
> > > >
> > > >
> > > > (Resending the reply as I messed up the last one, was not in plain text)
> > > >
> > > > I was curious, so I ran the same testing in a cgroup 2 levels deep
> > > > (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 for
> > > > 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).