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[82.17.115.212]) by smtp.gmail.com with ESMTPSA id d10-20020a056000114a00b002250c35826dsm13750502wrx.104.2022.09.26.02.20.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Sep 2022 02:20:05 -0700 (PDT) Date: Mon, 26 Sep 2022 10:20:04 +0100 From: Aaron Tomlin To: Hillf Danton Cc: frederic@kernel.org, mtosatti@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v8 5/5] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Message-ID: <20220926092004.to2zrcxjz5oj3lid@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: <20220924152227.819815-1-atomlin@redhat.com> <20220925010511.1482-1-hdanton@sina.com> MIME-Version: 1.0 In-Reply-To: <20220925010511.1482-1-hdanton@sina.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1664184009; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Epy/7zqqrTfa8taaB6YCWyslKlnR9eGzWLHjaNGqb/g=; b=FEYnVx1nqZ+6xVqNAmJXx8rLOqOZM7E78XcAsbenY3rh96VyTj9Sf8eneHEC3LRscfPdie pyudKtHoelvUhr4Z97tDujHUV4/C0pKR4Uq3pmdzyCo8D5pOKU3HryqQeIBAPhLVlOsMBS Taq6vgY85FCcxjhnV9Bkii2I1i/qkXQ= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=FEevcEME; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf11.hostedemail.com: domain of atomlin@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=atomlin@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664184009; a=rsa-sha256; cv=none; b=UIx115dD52mTC2waBLYaT4FQtqJUvqzL+jefuRcX/pkUMqvexVU7SpEVEsjnK7Tbq3e4Bq Aprcbx3xluDn0i6Y4cb3ooeQLiviU/lAOMaKfcIl4T2Ab/KJA31C51wBPpxJeKq1QnoDQG IYAtxlcVdC3/22Bt3W4Od0Cl00zNrjI= X-Rspam-User: X-Rspamd-Queue-Id: 7879F4000C X-Rspamd-Server: rspam01 X-Stat-Signature: 5wbcf6ujnhfpnxem578zi1qs83h1uffq Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=FEevcEME; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf11.hostedemail.com: domain of atomlin@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=atomlin@redhat.com X-HE-Tag: 1664184009-113428 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 Sun 2022-09-25 09:05 +0800, Hillf Danton wrote: > On 24 Sep 2022 16:24:41 +0100 Aaron Tomlin wrote: > > > > In the context of the idle task and an adaptive-tick mode/or a nohz_full > > CPU, quiet_vmstat() can be called: before stopping the idle tick, > > entering an idle state and on exit. In particular, for the latter case, > > when the idle task is required to reschedule, the idle tick can remain > > stopped and the timer expiration time endless i.e., KTIME_MAX. Now, > > indeed before a nohz_full CPU enters an idle state, CPU-specific vmstat > > counters should be processed to ensure the respective values have been > > reset and folded into the zone specific 'vm_stat[]'. That being said, it > > can only occur when: the idle tick was previously stopped, and > > reprogramming of the timer is not required. > > > > A customer provided some evidence which indicates that the idle tick was > > stopped; albeit, CPU-specific vmstat counters still remained populated. > > Thus one can only assume quiet_vmstat() was not invoked on return to the > > idle loop. > > Why did housekeeping CPUs fail to do their works, with this assumption > put aside? Hi Hillf, I'm not sure I understand your question. In this context, when tick processing is stopped, delayed work is not going to be handled until the CPU exits idle. Kind regards, -- Aaron Tomlin