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 43C88EB64DC for ; Mon, 3 Jul 2023 14:12:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229983AbjGCOMC (ORCPT ); Mon, 3 Jul 2023 10:12:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43436 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231157AbjGCOLr (ORCPT ); Mon, 3 Jul 2023 10:11:47 -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 F25B0E58 for ; Mon, 3 Jul 2023 07:11:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1688393471; 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=dBOERPIoo6ho6MdhXFVtaYCIHUOl3yOvK/q0qC4bZE0=; b=itxzg9gNJkQuI09sAXe766VhBgzHyArLxPfN544C31b4a3eFtnKHpZ5shQ0nTueX63K17W fpW5tFWN004wS9iNl/aYmYHQAclKSb0KABY9f0m9KhyeKaemy6xWEBosyhCyi8pgu83+27 O0Tp+JbZgZkAOa3PCKJ9//InsVuk+R8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-101-m6ED0EWVN--0u3qAhlIH7Q-1; Mon, 03 Jul 2023 10:11:05 -0400 X-MC-Unique: m6ED0EWVN--0u3qAhlIH7Q-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 BA61F810BB4; Mon, 3 Jul 2023 14:11:04 +0000 (UTC) Received: from lorien.usersys.redhat.com (unknown [10.39.194.77]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D098A1121314; Mon, 3 Jul 2023 14:11:00 +0000 (UTC) Date: Mon, 3 Jul 2023 10:10:56 -0400 From: Phil Auld To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Juri Lelli , Ingo Molnar , Daniel Bristot de Oliveira , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Ben Segall , Steven Rostedt , Mel Gorman , Frederic Weisbecker Subject: Re: [PATCH v4] Sched/fair: Block nohz tick_stop when cfs bandwidth in use Message-ID: <20230703141056.GA67396@lorien.usersys.redhat.com> References: <20230630135714.1018434-1-pauld@redhat.com> <20230630150641.GH2533791@hirez.programming.kicks-ass.net> <20230630152824.GC43299@lorien.usersys.redhat.com> <20230630160534.GA2534344@hirez.programming.kicks-ass.net> <20230630162910.GD43299@lorien.usersys.redhat.com> <20230703121009.GH4253@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230703121009.GH4253@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 03, 2023 at 02:10:09PM +0200 Peter Zijlstra wrote: > On Fri, Jun 30, 2023 at 12:29:10PM -0400, Phil Auld wrote: > > > I think you are agreeing that I need the pick next code but need to remove > > the hierarchy walks, right? > > Yeah, the dequeue case makes we have to care about pick, not sure we > then also need to care about sched_update_tick_dependency() though. > There is indeed a window where these two will 'race', but afaict it is > benign. > Hm, that's confusing. As I see it it's the enqueue case (0->1 mostly) where we need the check in pick. At that point in enqueue we only have a handle on ->curr which is the idle thread. For the dequeue case (2->1) we need the check in the sched_update_tick_dependency() path because if the 1 is the task on the cpu (and is staying there) then we'd otherwise clear the bit when we shouldn't (since we aren't going to go back through pick). I'm thinking that I'll try to set the bit in pick since we only care about it when it's the task on the cpu. That, I think, will simplify the code needed to update the bit when the quota is changed (to or from RUNTIME_INF). Setting the bit in enqueue/dequeue means updating it on all the queued task if it changes. Although I may clear it in dequeue just to not leave it around stale. Cheers, Phil --