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 B6DBBC433F5 for ; Wed, 27 Apr 2022 14:49:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238712AbiD0Owv (ORCPT ); Wed, 27 Apr 2022 10:52:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238693AbiD0Owq (ORCPT ); Wed, 27 Apr 2022 10:52:46 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C86113EF2E for ; Wed, 27 Apr 2022 07:49:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1651070973; 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=S8aF0VPL+4RQxQVtMfo2MXRnGizw2GrCzAZka9s1hOs=; b=G19+4oyUuDeDaMlw+9isrJr7y5Wz7Nd15BR8TrcyLrFqpng6wewFUB7L0X9nDvUkytxgFT n/oWqccr9vvrhr9FL1oVxQ8M4UC5Xy13Q697mGaZxW5ePc8DfeyCYejItQSFswyeMLDRrl ZZwVQWdcw75pYDMlwAv3twQLPTE5iXs= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-434-Y_zw08UAN02MVwYp7h4qaw-1; Wed, 27 Apr 2022 10:49:32 -0400 X-MC-Unique: Y_zw08UAN02MVwYp7h4qaw-1 Received: by mail-wm1-f70.google.com with SMTP id bh7-20020a05600c3d0700b003940829b48dso444167wmb.1 for ; Wed, 27 Apr 2022 07:49:32 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=S8aF0VPL+4RQxQVtMfo2MXRnGizw2GrCzAZka9s1hOs=; b=UWosbDpUtP/DycuRm5kaVywkhBvEfhj8xZP3f8gZxiksBZlfZORglkRoWBeHl5mur0 NHdKY8/kPlnbLUUrox1Ce8iCiK0GB3ChD4ng1xTkFsjtSnZlQYcfzud1dmDYWvYvFIWO rBvydkhZKUCjevDq6KA3HrBkpfo1NZ8gRo0DLsjM3sEK+upnCZpTUXrVe/CdwsnLPMge W4dL+VXEHDZhw7Z6TqJnKrGc1RH50rieKx0MhybMu3I56Tr16fn57iYNv+CxtdlKGgHc oRXXW2VAmni3YH6Hgam7nFRWfLum6YYflaiZVerCVaN6V6YZuZA7Dki5qVq+BoX33tbJ qMrg== X-Gm-Message-State: AOAM533cffLM70asdGSmaBZ1kOloJkOGN23lqCm3IMeuvmKPVBNemnbr PQ6d7TsBLZVl6Z8b39LgitQxZ0vM9jO9k8Im6B0Sz0ObdfbAdXiNgXeIDxDt02RKgLJQAyw2gPj 9FV1ZbvL32NbSsjz1f1F3IjY= X-Received: by 2002:a1c:f413:0:b0:37b:d1de:5762 with SMTP id z19-20020a1cf413000000b0037bd1de5762mr26699628wma.108.1651070971381; Wed, 27 Apr 2022 07:49:31 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxHKXnL5bdu2mcDHhShjxqFTABJ09lFyznMIxEOecs7P5FwwJkvPf6gtu0Nf8qzIhsHmQki6g== X-Received: by 2002:a1c:f413:0:b0:37b:d1de:5762 with SMTP id z19-20020a1cf413000000b0037bd1de5762mr26699608wma.108.1651070971212; Wed, 27 Apr 2022 07:49:31 -0700 (PDT) Received: from localhost (cpc111743-lutn13-2-0-cust979.9-3.cable.virginm.net. [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 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <875ymuy4h8.ffs@tglx> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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