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Thu, 24 Feb 2022 08:15:23 -0500 X-MC-Unique: E3FskdubMYSN1vTPcI5-nA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E2F5B1854E21; Thu, 24 Feb 2022 13:15:21 +0000 (UTC) Received: from fuller.cnet (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8936310631F7; Thu, 24 Feb 2022 13:15:19 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id D8300416D862; Thu, 24 Feb 2022 10:14:58 -0300 (-03) Date: Thu, 24 Feb 2022 10:14:58 -0300 From: Marcelo Tosatti To: Aaron Tomlin Cc: Frederic Weisbecker , Christoph Lameter , tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Phil Auld Subject: Re: [RFC PATCH] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Message-ID: References: <20220203214339.1889971-1-atomlin@redhat.com> <20220217124729.GA743618@lothringen> <20220217142615.xqtiydixvnumyvei@ava.usersys.com> <20220217163205.GA748087@lothringen> <20220218125454.utlgmuhijklzr3if@ava.usersys.com> <20220219154616.pwsvh445x3vn7ltf@ava.usersys.com> <20220224130014.rmhtx3xlepybuxn2@ava.usersys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220224130014.rmhtx3xlepybuxn2@ava.usersys.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D7381C000B X-Rspam-User: Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="bK//y7ov"; spf=none (imf28.hostedemail.com: domain of mtosatti@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=mtosatti@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: sfdww9at5qyw7gtu46i8s3u1eqry6fsu X-HE-Tag: 1645708528-429572 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 Thu, Feb 24, 2022 at 01:00:14PM +0000, Aaron Tomlin wrote: > On Thu 2022-02-24 09:27 -0300, Marcelo Tosatti wrote: > > But Aaron, vmstat_shepherd should be ensuring that per-CPU vmstat_update > > work are queued, if the per-CPU vmstat are out of sync. > > Hi Marcelo, > > Yes, I agree; albeit, as far as I understand, in the context of a nohz_full > CPU that has its scheduling-clock tick stopped, we cannot rely on any > deferred work. > > The purpose of my patch was to prevent a nohz_full CPU from entering idle > state when CPU-specific vmstat data is non-zero. > > > And: > > > > static void > > trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer) > > { > > if (!is_timers_nohz_active()) > > return; > > > > /* > > * TODO: This wants some optimizing similar to the code below, but we > > * will do that when we switch from push to pull for deferrable timers. > > */ > > if (timer->flags & TIMER_DEFERRABLE) { > > if (tick_nohz_full_cpu(base->cpu)) > > wake_up_nohz_cpu(base->cpu); > > return; > > } > > > > * @TIMER_DEFERRABLE: A deferrable timer will work normally when the > > * system is busy, but will not cause a CPU to come out of idle just > > * to service it; instead, the timer will be serviced when the CPU > > * eventually wakes up with a subsequent non-deferrable timer. > > > > You'd want that vmstat_update to execute regardless of whether there are > > armed non-deferrable timers. > > > > Should fix both 1 and 2 AFAICS. > > > > If I understand correctly, you are suggesting to switch to a non-deferred > timer for such work when the scheduling-clock tick is stopped? Indeed, it > would address both scenarios yet I'm not sure we'd want that due to the > performance impact which might be more than negligible. Aaron, If the per-CPU vmstat_update is limited to happen once per second, that shouldnt be a significant performance impact?