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

Yosry Ahmed
2023-10-12T23:29:35Z

[..]
> > >
> > > 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?
>
> I think it's reasonable.
>
> Especially comparing to how many cachelines we used to touch on the
> write side when all flushing happened there. This looks like a good
> trade-off to me.

Thanks.

Still wanting to figure out if this patch is what you suggested in our
previous discussion [1], to add a
Suggested-by if appropriate :)

[1]https://lore.kernel.org/lkml/20230913153758.GB45543@cmpxchg.org/