From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EE8FBC433EF for ; Wed, 27 Apr 2022 14:40:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238368AbiD0Ong (ORCPT ); Wed, 27 Apr 2022 10:43:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46038 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238330AbiD0Ond (ORCPT ); Wed, 27 Apr 2022 10:43:33 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9FE533E8F for ; Wed, 27 Apr 2022 07:40:21 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1651070420; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=3Bh8KuA/AAWOlDEUP/mUP1gM/q09Kmr3g1RCvu7cQIA=; b=F2bDEcJwCXciAlGCONIdOp8h76Zke4rhFmOCALvDr61Pje9+iX+kSae0g/0KZZEyWE4Lhw uu2YbfZ736RWAxpDMHT4rDXjhoymF68y70ALtVFpXDnDIj8LcQvHyIsjuVV6DFBV2D7Nd/ 9SZoe7dRZUVqo00THOHkboeJ/l0GDegoXpsIyxoJBo7EuGxyUngHXeVQSIn0XJCdyJb4n5 w+e2896jnBEf5Q3xE6sPCQM8c8iIDH35AQqZ3MhBmG9kNecefUnM53Tk4fWZsFYBtVuEGx /ZzrKuznkpH7cPQuu23Nm4RtOLEs33aWA8QMQvn3MAlIiLyxkUA46/kxQWYZYw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1651070420; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=3Bh8KuA/AAWOlDEUP/mUP1gM/q09Kmr3g1RCvu7cQIA=; b=OjMdNYOWGBflZsRQ25IzRNzYQtvuvcM5Q5QldqV9k/keM+3YEoPJ0ButUG4+nckzt3+Nfx vz4ZqhEaLaHTp7Cw== To: Aaron Tomlin , Marcelo Tosatti Cc: 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 In-Reply-To: <20220427115020.kyaxc5j67lq5zrfq@ava.usersys.com> 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> Date: Wed, 27 Apr 2022 16:40:19 +0200 Message-ID: <875ymuy4h8.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Thanks, tglx