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[82.17.115.212]) by smtp.gmail.com with ESMTPSA id f66-20020a1c3845000000b00393e84ea043sm1390797wma.44.2022.04.27.04.50.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Apr 2022 04:50:21 -0700 (PDT) Date: Wed, 27 Apr 2022 12:50:20 +0100 From: Aaron Tomlin To: Marcelo Tosatti Cc: Peter Zijlstra , Christoph Lameter , frederic@kernel.org, tglx@linutronix.de, mingo@kernel.org, pauld@redhat.com, neelx@redhat.com, oleksandr@natalenko.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH v3] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Message-ID: <20220427115020.kyaxc5j67lq5zrfq@ava.usersys.com> X-PGP-Key: http://pgp.mit.edu/pks/lookup?search=atomlin%40redhat.com X-PGP-Fingerprint: 7906 84EB FA8A 9638 8D1E 6E9B E2DE 9658 19CC 77D6 References: <20220422193647.3808657-1-atomlin@redhat.com> <20220425113909.u3smtztp66svlw4o@ava.usersys.com> <20220425132700.GK2731@worktop.programming.kicks-ass.net> <20220425141717.vw2jfnn3zp6c5ib2@ava.usersys.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 8C0EFA0056 X-Stat-Signature: wmxkinmjp9a4qbnpg6jd97o8duitrsya Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=JcJ0GTTC; spf=none (imf15.hostedemail.com: domain of atomlin@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=atomlin@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1651060222-548073 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: On Mon 2022-04-25 16:21 -0300, Marcelo Tosatti wrote: > > Hi Peter, Christoph, > > > > Indeed. Which was why I decided, initially, against the general-purpose > > case/or approach. Personally, I would prefer to keep this somewhat > > restrictive to nohz. > > Is there anything that prevents a nohz full CPU from running an > application with short and frequent idling? Hi Marcelo, I'm not sure I understand the question; albeit, if I understand correctly, yes: the scheduling-clock tick, if it was stopped. Yet I believe this behaviour is correct. Consider the following example: When a CFS task is moved/or migrated to a nohz_full CPU that was previously idle and had its tick stopped, if its the only task on the run-queue then it is possible that the idle task may not restart the tick (see __tick_nohz_full_update_tick()). Thus once the CFS task exits manual intervention i.e. a reschedule IPI to wake the idle task, would be required to run again, on the same CPU. Kind regards, -- Aaron Tomlin