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[82.17.115.212]) by smtp.gmail.com with ESMTPSA id n4-20020a1ca404000000b00392965e41d6sm1707631wme.39.2022.04.27.07.49.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Apr 2022 07:49:30 -0700 (PDT) Date: Wed, 27 Apr 2022 15:49:27 +0100 From: Aaron Tomlin To: Thomas Gleixner Cc: Marcelo Tosatti , Peter Zijlstra , Christoph Lameter , frederic@kernel.org, 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: <20220427144927.c5as3sa4mheawea5@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> <20220427115020.kyaxc5j67lq5zrfq@ava.usersys.com> <875ymuy4h8.ffs@tglx> MIME-Version: 1.0 In-Reply-To: <875ymuy4h8.ffs@tglx> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Stat-Signature: gi9rmjui7u33fts36x5gyhp4uniiwney X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9587C40055 Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=eyQqYLVo; spf=none (imf27.hostedemail.com: domain of atomlin@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=atomlin@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-HE-Tag: 1651070974-888934 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 Wed 2022-04-27 16:40 +0200, Thomas Gleixner wrote: > On Wed, Apr 27 2022 at 12:50, Aaron Tomlin wrote: > > On Mon 2022-04-25 16:21 -0300, Marcelo Tosatti wrote: > >> Is there anything that prevents a nohz full CPU from running an > >> application with short and frequent idling? > > > > 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. > > When the task exits and the tick was stopped, why should idle restart > the tick? There is nothing to do, so what? Hi Thomas, Indeed. As per my response, I do not see an issue. Perhaps I misunderstood Marcelo's question, no? Kind regards, -- Aaron Tomlin