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 6B104C433F5 for ; Wed, 30 Mar 2022 18:40:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350309AbiC3SmM (ORCPT ); Wed, 30 Mar 2022 14:42:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53582 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350353AbiC3Sl7 (ORCPT ); Wed, 30 Mar 2022 14:41:59 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8FE176CA4D for ; Wed, 30 Mar 2022 11:37:54 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 1FB0BB81E21 for ; Wed, 30 Mar 2022 18:37:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 428F5C340EC; Wed, 30 Mar 2022 18:37:50 +0000 (UTC) Date: Wed, 30 Mar 2022 14:37:48 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: Chengming Zhou , mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org, duanxiongchun@bytedance.com, songmuchun@bytedance.com, Frederic Weisbecker Subject: Re: [External] Re: [PATCH] sched/fair: fix broken bandwidth control with nohz_full Message-ID: <20220330143748.37f4804c@gandalf.local.home> In-Reply-To: <20220330182327.GO8939@worktop.programming.kicks-ass.net> References: <20220328110751.39987-1-zhouchengming@bytedance.com> <20220328132047.GD8939@worktop.programming.kicks-ass.net> <6fc49cff-f8a1-8b09-5a25-a64e5d07d258@bytedance.com> <20220328124454.08ab6126@gandalf.local.home> <20220330182327.GO8939@worktop.programming.kicks-ass.net> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 30 Mar 2022 20:23:27 +0200 Peter Zijlstra wrote: > > Chengming brought up VMs. That's a case to want to control the bandwidth, > > but also not interrupt them with timer interrupts when they are running as > > the top priority task on a CPU. > > It's CFS, there is nothing top priority about that. If there's only one task running on a CPU, even with CFS, why do we need a tick? Look, we have a host that is doing nothing but running VMs. Could be a single VM. The host doesn't even have disk, it just runs on from initrd, and the user is actually just logging into a guest. Why should the host be triggering a tick when running this VM, which is the only thing that is running on the host? Yeah, it's CFS, or does CFS have to have a tick? even when there's nothing else on the CPU? -- Steve