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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6E67C47255 for ; Mon, 11 May 2020 17:14:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC815206D7 for ; Mon, 11 May 2020 17:14:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="DuLILASw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730811AbgEKROb (ORCPT ); Mon, 11 May 2020 13:14:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37064 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729730AbgEKROb (ORCPT ); Mon, 11 May 2020 13:14:31 -0400 Received: from mail-lf1-x142.google.com (mail-lf1-x142.google.com [IPv6:2a00:1450:4864:20::142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AAD9CC061A0C for ; Mon, 11 May 2020 10:14:29 -0700 (PDT) Received: by mail-lf1-x142.google.com with SMTP id a9so8157214lfb.8 for ; Mon, 11 May 2020 10:14:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=6sb4ra23XyszA4AK865cfO4rcCikUbslE1rJprkW4Zw=; b=DuLILASwN0JEFSsNdlE/zTNjFmhZMRc2njVHMcx1kOx69kYDSl/ekdJxzBjvueJUcw 3cAaqu9+8LKiUA4nWtBJvax2TNuqqAQXCZFZ3TpwVDdRZCeyzzfj8Pk8e/Q2r8gLeWUv mukZEmvPzbfIwuswhAW6jTlUge0tvpLYg+k037F0vR1EAfKqdeB2R5lm1Fxk7ygIZubI lSvraSoYjTmmHFgZy+pIq59ePNcwJmLjoBLWj0pVTlbj7ihhACY9HhtuIru3jIhD8RQh CxPTWOgXGRgtJbON5ZH8sYRvSoWXxE7HdWsPDiru2hukG3GKNlW8sKIBSKln1eG6wPr7 WNvg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=6sb4ra23XyszA4AK865cfO4rcCikUbslE1rJprkW4Zw=; b=HtvCbaTsEduv09mlk0sE4g1kdIPGaOSCL5sigDtdfxgg0WShoximWjKUa0l4OC13qr 4dGG8VrengvutLQ9Em2Q2x3SylGiLM0cZ3aorB467eyYYdsTQdS0m7ZwVZRV0A0CAhTo 6q0GdrYKDiQq7HZfQ8WXTLlzUyESL4ADfK/VmZdkZtE6Gu4inXJsYqs254wnEfOydDUO kv4WlO+3RNuTXGlVIcwgpGILszMYnpLmvEOlHb2eVWA4YyQvnrRgfvvRK996c9aPQvhj el38WkldwwLCar/4c8sRsyHXbUB2P3+ltHPeglhkWXb8YoYE6lMVThMeJ/wKdPL7qQDh X9OA== X-Gm-Message-State: AOAM532hzauFjFNzSg3BsFOONZKlIkEfAuGxaZHPX+vYvakvwp/st9mI o/Qtz9AvlaW3FhVPH5oM+QBtCG7ofN58hzZxI97e2w== X-Google-Smtp-Source: ABdhPJxNqtxcMaJeK+AjAuHFyWUUOW8MA/tr2g4pW4qTtzOkYgd4k2IOz19My3C6u4IeoWqCe6LNqHqSv64uRIGkzlg= X-Received: by 2002:a05:6512:44e:: with SMTP id y14mr11674238lfk.190.1589217267017; Mon, 11 May 2020 10:14:27 -0700 (PDT) MIME-Version: 1.0 References: <20200506141821.GA9773@lorien.usersys.redhat.com> <20200507203612.GF19331@lorien.usersys.redhat.com> <20200508151515.GA25974@geo.homenetwork> <20200508170213.GA27353@geo.homenetwork> <801229de-200d-c9d5-7fd3-8556c5abc064@arm.com> <2a45d9ac-1d8a-da8c-a743-7e1f87724635@arm.com> In-Reply-To: <2a45d9ac-1d8a-da8c-a743-7e1f87724635@arm.com> From: Vincent Guittot Date: Mon, 11 May 2020 19:14:15 +0200 Message-ID: Subject: Re: [PATCH v2] sched/fair: Fix enqueue_task_fair warning some more To: Dietmar Eggemann Cc: Tao Zhou , Phil Auld , Peter Zijlstra , linux-kernel , Ingo Molnar , Juri Lelli , Tao Zhou Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 11 May 2020 at 19:02, Dietmar Eggemann wrote: > > On 11/05/2020 14:12, Vincent Guittot wrote: > > On Mon, 11 May 2020 at 12:39, Dietmar Eggemann wrote: > >> > >> On 11/05/2020 11:36, Vincent Guittot wrote: > >>> On Mon, 11 May 2020 at 10:40, Dietmar Eggemann wrote: > >>>> > >>>> On 08/05/2020 19:02, Tao Zhou wrote: > >>>>> On Fri, May 08, 2020 at 05:27:44PM +0200, Vincent Guittot wrote: > >>>>>> On Fri, 8 May 2020 at 17:12, Tao Zhou wrote: > >>>>>>> > >>>>>>> Hi Phil, > >>>>>>> > >>>>>>> On Thu, May 07, 2020 at 04:36:12PM -0400, Phil Auld wrote: > >>>>>>>> sched/fair: Fix enqueue_task_fair warning some more > >> > >> [...] > >> > >>>> I'm not 100% sure if this is exactly what Tao pointed out here but I > >>>> also had difficulties understanding understanding how this patch works: > >>>> > >>>> p.se > >>>> | > >>>> __________________| > >>>> | > >>>> V > >>>> cfs_c -> tg_c -> se_c (se->on_rq = 1) > >>>> | > >>>> __________________| > >>>> | > >>>> v > >>>> cfs_b -> tg_b -> se_b > >>>> | > >>>> __________________| > >>>> | > >>>> V > >>>> cfs_a -> tg_a -> se_a > >>>> | > >>>> __________________| > >>>> | > >>>> V > >>>> cfs_r -> tg_r > >>>> | > >>>> V > >>>> rq > >>>> > >>> > >>> In your example, which cfs_ rq has been throttled ? cfs_a ? > >> > >> Yes, cfs_a. 0xffffa085e48ce000 in Phil's trace. > >> > >>> > >>>> (1) The incomplete update happens with cfs_c at the end of > >>>> enqueue_entity() in the first loop because of 'if ( .... || > >>>> cfs_bandwidth_used())' (cfs_b->on_list=0 since cfs_a is throttled) > >>> > >>> so cfs_c is added with the 1st loop > >> > >> Yes. > >> > >>>> (2) se_c breaks out of the first loop (se_c->on_rq = 1) > >>>> > >>>> (3) With the patch cfs_b is added back to the list. > >>>> But only because cfs_a->on_list=1. > >>> > >>> hmm I don't understand the link between cfs_b been added and cfs_a->on_list=1 > >> > >> cfs_b, 0xffffa085e48ce000 is the one which is now added in the 2. loop. > >> > >> Isn't the link between cfs_b and cfs_a the first if condition in > > > > on_list is only there to say if the cfs_rq is already in the list but > > there is not dependency with the child > > Yes, I agree. But coming back to what the patch does in the example: > > W/ the patch, list_add_leaf_cfs_rq() is now called for cfs_b and since > cfs_b->tg->parent->cfs_a and cfs_a->on_list=1 the 'branch is now > connected' which means 'rq->tmp_alone_branch = &rq->leaf_cfs_rq_list'. > > I.e. assert_list_leaf_cfs_rq() at the end of enqueue_task_fair() is not > barfing anymore. > > W/o the patch, list_add_leaf_cfs_rq() called w/ cfs_c left the 'branch > open', it's not called on cfs_b and since cfs_a->on_list=1, the 3rd > for_each_sched_entity() in enqueue_task_fair() doesn't 'connect the > branch' so the assert fires. > > What I don't immediately see is how can cfs_a be throttled (which causes > cfs_b -> cfs_c being a throttled hierarchy) and be on the list > (cfs_a->on_list=1) at the same time. > > So the only thing how this could happen is when there was a task enqueue > in a parallel cfs_b' (another child of cfs_a) sub hierarchy just before > the example. Yes. A task has been enqueued on another child (cfs_b') and cfs_a has been be added back to ensure that cfs are correctly ordered > > >> list_add_leaf_cfs_rq(): > >> > >> if (cfs_rq->tg->parent && > >> cfs_rq->tg->parent->cfs_rq[cpu]->on_list) > >> > >> to 'connect the branch' or not (default, returning false case)? > >> > > > > In your example above if the parent is already on the list then we > > know where to insert the child. > > True, we go the 2nd if() condition in list_add_leaf_cfs_rq(). > > >>> cfs_b is added with 2nd loop because its throttle_count > 0 due to > >>> cfs_a been throttled (purpose of this patch) > >>> > >>>> > >>>> But since cfs_a is throttled it should be cfs_a->on_list=0 as well. > >>> > >>> So 2nd loop breaks because cfs_a is throttled > >> > >> Yes. > >> > >>> The 3rd loop will add cfs_a > >> > >> Yes, but in the example, cfs_a->on_list=1, so we bail out of > >> list_add_leaf_cfs_rq() early. > > > > Because the cfs_rq is on the list already so we don't have to add it > > Yes. > > [...]