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Message-ID: <ZEqh5qzFZFrSUja/@tpad>
Date: Thu, 27 Apr 2023 13:25:10 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Michal Hocko <mhocko@...e.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
Frederic Weisbecker <frederic@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>,
Aaron Tomlin <atomlin@...mlin.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Russell King <linux@...linux.org.uk>,
Huacai Chen <chenhuacai@...nel.org>,
Heiko Carstens <hca@...ux.ibm.com>, x86@...nel.org
Subject: Re: [PATCH v7 00/13] fold per-CPU vmstats remotely
On Thu, Apr 27, 2023 at 10:39:29AM +0200, Michal Hocko wrote:
> On Wed 26-04-23 13:10:54, Marcelo Tosatti wrote:
> [...]
> > "To test the performance difference, a page allocator microbenchmark:
> > https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/mm/bench/page_bench01.c
> > with loops=1000000 was used, on Intel Core i7-11850H @ 2.50GHz.
> >
> > For the single_page_alloc_free test, which does
> >
> > /** Loop to measure **/
> > for (i = 0; i < rec->loops; i++) {
> > my_page = alloc_page(gfp_mask);
> > if (unlikely(my_page == NULL))
> > return 0;
> > __free_page(my_page);
> > }
> >
> > Unit is cycles.
> >
> > Vanilla Patched Diff
> > 115.25 117 1.4%"
> >
> > To be honest, that 1.4% difference was not stable but fluctuated between
> > positive and negative percentages (so the performance difference was in
> > the noise).
> >
> > So performance is not a decisive factor in this case.
>
> It is not neglible considering that majority worklods will not benefit
> from this change. You are clearly ignoring that vmstat code has been
> highly optimized for local per-cpu access exactly to avoid locked
> operations and cache line bouncing.
> --
> Michal Hocko
> SUSE Labs
Again, the values fluctuate between positive and negative
performance difference (i happen to have copied a positive value).
So the performance difference is in the noise (its not stable at 1.4%),
but rather close to 0%.
So the data is showing that there is no negative performance impact.
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