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Tue, 01 Apr 2025 08:00:02 -0700 (PDT) Date: Tue, 1 Apr 2025 17:00:00 +0200 From: Michal =?utf-8?Q?Koutn=C3=BD?= To: Mateusz Guzik Cc: Yosry Ahmed , Greg Thelen , Tejun Heo , Johannes Weiner , Andrew Morton , Eric Dumazet , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Dumazet Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu) Message-ID: <3mc7l6otsn4ufmyaiuqgpf64rfcukilgpjainslniwid6ajqm7@ltxbi5qennh7> References: <20250319071330.898763-1-gthelen@google.com> <2vznaaotzkgkrfoi2qitiwdjinpl7ozhpz7w6n7577kaa2hpki@okh2mkqqhbkq> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="lhtzb6rhkzysoxx3" Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 6E95240009 X-Stat-Signature: 53f88i8p8ch5rptywyz6gzup6wjjtohx X-Rspam-User: X-HE-Tag: 1743519604-987872 X-HE-Meta: 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 xYbFccsm 7p7e6BZ3nFA9B9z3lH8hveJQ0/WwRNDSe7eHQJJQLprcoJN4YzMLZAdcqCnbD8fsOyIXnj+DrS5LYHT0w+XT7toQrzWdz0niTCVoSrlXnNpY7nlshZY5+DXmdYsnJ9F2oAzVl3db4orr8bYity1HWKr6c5uRtSVu7LV5TvZkPjFnhBQ2gUkSE0BIix4d8qfN0pBG9dsLlz4+/K6d4MMntk/9QUJh3lwiNen7PfB8KgbicgZD7TdP0moeyxezEHyUt5goAjgriSRp9I3C2lDJRcf0eduw/w/vn/onQN3UkCvlfMR3YIzvcVI3xZwdTzJhC3HUbx0OC35k4hd6UrETRDcj9QoShzSIfPSF+HyZcQmaSD5OK7uysa49sotsqUaFJFuN5I4F5R8ru1rxSlmDtYCqqGb1Y3prtAFXazprM1GGvAuv+uWC1e+PY8EyatqkmfZBirajxHitWi4jmV3YApmnJF4z43r41K64HzOENG/C1dfoepMAUaxjP5a4Q0AYlAxk9 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --lhtzb6rhkzysoxx3 Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu) MIME-Version: 1.0 Hello Mateusz. On Thu, Mar 27, 2025 at 06:47:56PM +0100, Mateusz Guzik wrote: > I feel compelled to note atomics on x86-64 were expensive for as long > as the architecture was around so I'm confused what's up with the > resistance to the notion that they remain costly even with modern > uarchs. If anything, imo claims that they are cheap require strong > evidence. I don't there's strong resistance, your measurements show that it's not negligible under given conditions. The question is -- how much benefit would flushers have in practice with coalesced unlock-locks. There is the approach now with releasing for each CPU that is simple and benefits latency of irq dependants. If you see practical issues with the limited throughputs of stat readers (or flushers in general) because of this, please send a patch for discussion that resolves it while preserving (some of) the irq freedom. Also there is ongoing work of splitting up flushing per controller -- I'd like to see whether the given locks become "small" enough to require no _irq exclusion at all during flushing. Michal --lhtzb6rhkzysoxx3 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTd6mfF2PbEZnpdoAkt3Wney77BSQUCZ+v/bgAKCRAt3Wney77B SXa6AP9UY9UpmP/PK0EYqNZ2VFIM6F2xZ1gnkE8mn3oo41sCUwEAlM/YE51Kwt4+ B5zUl6bs53aI6sxUZYxjYcpl1p3zbw0= =QqaZ -----END PGP SIGNATURE----- --lhtzb6rhkzysoxx3--