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From:   Andrey Konovalov <andreyknvl@gmail.com>
Date:   Wed, 13 Sep 2023 19:08:56 +0200
Message-ID: <CA+fCnZdAUo1CKDK4kiUyR+Fxc_F++CFezanPDVujx3u7fBmw=A@mail.gmail.com>
Subject: Re: [PATCH 11/15] stackdepot: use read/write lock
To:     Marco Elver <elver@google.com>
Cc:     andrey.konovalov@linux.dev,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        Evgenii Stepanov <eugenis@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
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On Tue, Sep 5, 2023 at 6:19=E2=80=AFPM Marco Elver <elver@google.com> wrote=
:
>
> > Good suggestion. I propose that we keep the rwlock for now, and I'll
> > check whether the performance is better with percpu-rwsem once I get
> > to implementing and testing the performance changes. I'll also check
> > whether percpu-rwsem makes sense for stack ring in tag-based KASAN
> > modes.
>
> I think it's quite obvious that the percpu-rwsem is better. A simple
> experiment is to measure the ratio of stackdepot hits vs misses. If
> the ratio is obviously skewed towards hits, then I'd just go with the
> percpu-rwsem.
>
> The performance benefit may not be measurable if you use a small system.

I started looking into using percpu-rwsem, but it appears that it
doesn't have the irqsave/irqrestore API flavor. I suspect that it
shouldn't be hard to add it, but I'd rather not pursue this as a part
of this series.

So I still propose to keep the rwlock for now, and switch to
percpu-rwsem later together with the other perf changes.