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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 18A8BC46460 for ; Tue, 14 Aug 2018 16:49:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C5EE121728 for ; Tue, 14 Aug 2018 16:49:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C5EE121728 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732564AbeHNThG (ORCPT ); Tue, 14 Aug 2018 15:37:06 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:45936 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732280AbeHNThF (ORCPT ); Tue, 14 Aug 2018 15:37:05 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4FDFD18A; Tue, 14 Aug 2018 09:49:10 -0700 (PDT) Received: from e110439-lin (e110439-lin.emea.arm.com [10.4.12.126]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A24BF3F5BD; Tue, 14 Aug 2018 09:49:07 -0700 (PDT) Date: Tue, 14 Aug 2018 17:49:05 +0100 From: Patrick Bellasi To: Dietmar Eggemann Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan Subject: Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting Message-ID: <20180814164905.GG2605@e110439-lin> References: <20180806163946.28380-1-patrick.bellasi@arm.com> <20180806163946.28380-4-patrick.bellasi@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Dietmar! On 14-Aug 17:44, Dietmar Eggemann wrote: > On 08/06/2018 06:39 PM, Patrick Bellasi wrote: [...] > >+/** > >+ * uclamp_cpu_put_id(): decrease reference count for a clamp group on a CPU > >+ * @p: the task being dequeued from a CPU > >+ * @cpu: the CPU from where the clamp group has to be released > >+ * @clamp_id: the utilization clamp (e.g. min or max utilization) to release > >+ * > >+ * When a task is dequeued from a CPU's RQ, the CPU's clamp group reference > >+ * counted by the task is decreased. > >+ * If this was the last task defining the current max clamp group, then the > >+ * CPU clamping is updated to find the new max for the specified clamp > >+ * index. > >+ */ > >+static inline void uclamp_cpu_put_id(struct task_struct *p, > >+ struct rq *rq, int clamp_id) > >+{ > >+ struct uclamp_group *uc_grp; > >+ struct uclamp_cpu *uc_cpu; > >+ unsigned int clamp_value; > >+ int group_id; > >+ > >+ /* No task specific clamp values: nothing to do */ > >+ group_id = p->uclamp[clamp_id].group_id; > >+ if (group_id == UCLAMP_NOT_VALID) > >+ return; > >+ > >+ /* Decrement the task's reference counted group index */ > >+ uc_grp = &rq->uclamp.group[clamp_id][0]; > >+#ifdef SCHED_DEBUG > >+ if (unlikely(uc_grp[group_id].tasks == 0)) { > >+ WARN(1, "invalid CPU[%d] clamp group [%d:%d] refcount\n", > >+ cpu_of(rq), clamp_id, group_id); > >+ uc_grp[group_id].tasks = 1; > >+ } > >+#endif > > This one indicates that there are some holes in your ref-counting. Not really, this has been added not because I've detected a refcount issue... but because it was suggested as a possible safety check in a previous code review comment: https://lore.kernel.org/lkml/20180720151156.GA31421@e110439-lin/ > It's probably easier to debug that there is still a task but the > uc_grp[group_id].tasks value == 0 (A). I assume the other problem exists as > well, i.e. last task and uc_grp[group_id].tasks > 1 (B)? > > You have uclamp_cpu_[get/put](_id)() in [enqueue/dequeue]_task. > > Patch 04/14 introduces its use in uclamp_task_update_active(). > > Do you know why (A) (and (B)) are happening? I've never saw that warning in my tests so far so, again, the warning is there just to support testing/debugging when refcounting code is/will be touched in the future. That's also the reason why is SCHED_DEBUG protected. > >+ uc_grp[group_id].tasks -= 1; > >+ > >+ /* If this is not the last task, no updates are required */ > >+ if (uc_grp[group_id].tasks > 0) > >+ return; > >+ > >+ /* > >+ * Update the CPU only if this was the last task of the group > >+ * defining the current clamp value. > >+ */ > >+ uc_cpu = &rq->uclamp; > >+ clamp_value = uc_grp[group_id].value; > >+ if (clamp_value >= uc_cpu->value[clamp_id]) > > 'clamp_value > uc_cpu->value[clamp_id]' should indicate another > inconsistency in the uclamp machinery, right? Here you right, I would say that it should always be: clamp_value <= uc_cpu->value[clamp_id] since this matches the update done at the end of uclamp_cpu_get_id(): if (uc_cpu->value[clamp_id] < clamp_value) uc_cpu->value[clamp_id] = clamp_value; Perhaps we can add another safety check here, similar to the one above, to have something like: clamp_value = uc_grp[group_id].value; #ifdef SCHED_DEBUG if (unlikely(clamp_value > uc_cpu->value[clamp_id])) { WARN(1, "invalid CPU[%d] clamp group [%d:%d] value\n", cpu_of(rq), clamp_id, group_id); #endif if (clamp_value == uc_cpu->value[clamp_id]) uclamp_cpu_update(rq, clamp_id); -- #include Patrick Bellasi