linux-kernel - Re: [linus:master] [mm] f1a7941243: unixbench.score -19.2% regression

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Message-ID: <CALvZod7TuaJ7pCc2nJKehwGkcuvsvjdL+4hs6qC3bZsOmGzXzg@mail.gmail.com>
Date:   Tue, 31 Jan 2023 10:26:52 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>, Tejun Heo <tj@...nel.org>,
        Dennis Zhou <dennis@...nel.org>
Cc:     kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
        lkp@...el.com, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
        ying.huang@...el.com, feng.tang@...el.com,
        zhengjun.xing@...ux.intel.com, fengwei.yin@...el.com
Subject: Re: [linus:master] [mm] f1a7941243: unixbench.score -19.2% regression

+per-cpu memory maintainers for FYI.

Thread started at
https://lore.kernel.org/linux-mm/202301301057.e55dad5b-oliver.sang@intel.com/

On Mon, Jan 30, 2023 at 9:57 PM Shakeel Butt <shakeelb@...gle.com> wrote:
>
[...]
> >
> > We could cut down the number of calls to pcpu_alloc() by a factor of 4
> > by having a pcpu_alloc_bulk() that would allocate all four RSS counters
> > at once.
> >
> > Just throwing out ideas ...
>
> Thanks, I will take a stab at pcpu_alloc_bulk() and will share the
> result tomorrow.
>

OK, not a one day effort.

Andrew, which option do you prefer?

1. Keep the patches as the test workload (fork ping pong) is not a
representative of real world workload and work on improving
pcpu_alloc() for 6.4+.

2. Revert the patches for now, improve pcpu_alloc() and re-introduce
the patches once we confirm that fork-ping-pong is not regressed
anymore.

thanks,
Shakeel