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 00933EB64D8 for ; Thu, 22 Jun 2023 15:46:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230243AbjFVPqR (ORCPT ); Thu, 22 Jun 2023 11:46:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229659AbjFVPqP (ORCPT ); Thu, 22 Jun 2023 11:46:15 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BDE57EA for ; Thu, 22 Jun 2023 08:45:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1687448731; 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=U0NqUtHzBlRyAKRtYPhN8+KmHj1spzFJlhdBUav2GW4=; b=NVv02qOzB0QPm8XcEyBGQTGBDI5bKQdjNQ0fjjJ0VeE3XyV3faj+wYY3CtBiFoKIb5gh4h OvPSL8dUYhu5FNF1bU/lDI1RhiToNDsc3OGLfnF967npCMMGftew2hLr9wndhLUc+1gexs EBuPe/P/ECywgXY2Nu6upyReEgdDHrc= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-557-dM1pfrdXOrK9OUwCA0yK1w-1; Thu, 22 Jun 2023 11:45:27 -0400 X-MC-Unique: dM1pfrdXOrK9OUwCA0yK1w-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id EF51E3813F2D; Thu, 22 Jun 2023 15:45:15 +0000 (UTC) Received: from lorien.usersys.redhat.com (unknown [10.22.9.68]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A2C9C112132C; Thu, 22 Jun 2023 15:45:12 +0000 (UTC) Date: Thu, 22 Jun 2023 11:44:58 -0400 From: Phil Auld To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Juri Lelli , Ingo Molnar , Daniel Bristot de Oliveira , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Ben Segall , Mel Gorman Subject: Re: [PATCH] Sched/fair: Block nohz tick_stop when cfs bandwidth in use Message-ID: <20230622154458.GD727646@lorien.usersys.redhat.com> References: <20230622132751.2900081-1-pauld@redhat.com> <20230622102216.3b841f80@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230622102216.3b841f80@gandalf.local.home> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 22, 2023 at 10:22:16AM -0400 Steven Rostedt wrote: > On Thu, 22 Jun 2023 09:27:51 -0400 > Phil Auld wrote: > > > CFS bandwidth limits and NOHZ full don't play well together. Tasks > > can easily run well past their quotas before a remote tick does > > accounting. This leads to long, multi-period stalls before such > > tasks can run again. Currentlyi, when presented with these conflicting > > requirements the scheduler is favoring nohz_full and letting the tick > > be stopped. However, nohz tick stopping is already best-effort, there > > are a number of conditions that can prevent it, whereas cfs runtime > > bandwidth is expected to be enforced. > > > > Make the scheduler favor bandwidth over stopping the tick by setting > > TICK_DEP_BIT_SCHED when the only running task is a cfs task with > > runtime limit enabled. > > > > Add sched_feat HZ_BW (off by default) to control this behavior. > > So the tl;dr; is: "If the current task has a bandwidth limit, do not disable > the tick" ? > Yes. W/o the tick we can't reliably support/enforce the bandwidth limit. Cheers, Phil > -- Steve > --