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Wed, 13 Sep 2023 10:09:07 -0700 (PDT) MIME-Version: 1.0 References: <6db160185d3bd9b3312da4ccc073adcdac58709e.1693328501.git.andreyknvl@google.com> In-Reply-To: From: Andrey Konovalov Date: Wed, 13 Sep 2023 19:08:56 +0200 Message-ID: Subject: Re: [PATCH 11/15] stackdepot: use read/write lock To: Marco Elver Cc: andrey.konovalov@linux.dev, Alexander Potapenko , Dmitry Vyukov , Vlastimil Babka , kasan-dev@googlegroups.com, Evgenii Stepanov , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: eusudpwpto71xp5xh56hjuceapmjn5cu X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 68BAB4000A X-Rspam-User: X-HE-Tag: 1694624948-861281 X-HE-Meta: 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 1ZQd+Fus dLkIvFkn2BUGC713+TY9D3qxcydRDagK+WmAY9g9UepBkHp7CrN5Z0ntwGo6qYXkaK9SKhRNDvBEcVcYeeX8pGlc4b5xxoAPvGdCHvCoSvOJKyCzvAvFhasX/vlcHvKe8SGTMpvDFNfEcxnDxlsw0VZT3l8UalAdkAoyFkmoWGgd8W0oDocP1NhVB/DiH7kqchO6pvEVhMm5E12kvciY3escwu9Uu+KkUok8TCk2qwy3p7jQ6tonm/BMnh2LfjOJil1dlBIdHKCB06yYFbSCAAv9wehY2D7DCfbArEiBKxM0QkgzwnJyh5AJK0d8ywjeBjfqWORL6QV1SLHi2yFDRwKhIDkoW40KfqXug0XxNA3g9ns3nm+1Eus0dOQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.121417, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 5, 2023 at 6:19=E2=80=AFPM Marco Elver 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.