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