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=-10.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 DAD66C6377D for ; Thu, 22 Jul 2021 08:47:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C39DA6128C for ; Thu, 22 Jul 2021 08:47:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231162AbhGVIG7 (ORCPT ); Thu, 22 Jul 2021 04:06:59 -0400 Received: from foss.arm.com ([217.140.110.172]:47700 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230314AbhGVIG4 (ORCPT ); Thu, 22 Jul 2021 04:06:56 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E5605D6E; Thu, 22 Jul 2021 01:47:31 -0700 (PDT) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3ABA03F73D; Thu, 22 Jul 2021 01:47:30 -0700 (PDT) Subject: Re: [PATCH v4 1/2] sched: Fix UCLAMP_FLAG_IDLE setting To: Quentin Perret Cc: mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, qais.yousef@arm.com, rickyiu@google.com, wvw@google.com, patrick.bellasi@matbug.net, xuewen.yan94@gmail.com, linux-kernel@vger.kernel.org, kernel-team@android.com References: <20210719161656.3833943-1-qperret@google.com> <20210719161656.3833943-2-qperret@google.com> <7ef85d3f-fd2b-a192-07ef-3431b33d06ce@arm.com> From: Dietmar Eggemann Message-ID: Date: Thu, 22 Jul 2021 10:47:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/07/2021 15:09, Quentin Perret wrote: > Hi Dietmar, > > On Wednesday 21 Jul 2021 at 12:07:04 (+0200), Dietmar Eggemann wrote: >> On 19/07/2021 18:16, Quentin Perret wrote: >>> The UCLAMP_FLAG_IDLE flag is set on a runqueue when dequeueing the last >>> active task to maintain the last uclamp.max and prevent blocked util >> >> s/active/runnable ? > > 'active' should still be correct here no? We enter uclamp_rq_max_value() > -> uclamp_idle_value() when the last _active_ uclamp_se is decremented, > and when all the buckets are empty, so I think that works? Ah, it this uclamp ative `p->uclamp[clamp_id].active` which is set with `bucket->tasks` in uclamp_rq_[inc/dec]_id. Maybe add: last (uclamp) active task, i.e. (bucket.tasks == 0 for all bucket_id's) ... ? >>> from suddenly becoming visible. >>> >> >> [...] >> >> IMHO, the main argument in v3 to do the clearing outside >> uclamp_rq_inc_id() was a possible order change in `for_each_clamp_id()`. >> So setting/clearing `rq->uclamp_flags` (UCLAMP_FLAG_IDLE) on UCLAMP_MAX >> (currently the highest Uclamp constraint (UCLAMP_CNT-1)) could be >> incorrect when UCLAMP_MIN and UCLAMP_MAX change place because the >> same `rq->uclamp_flags` value is needed for both Uclamp constraint >> values. >> >> What about decoupling rq->uclamp_flags` handling from UCLAMP_MAX and >> doing this for 'UCLAMP_CNT - 1', i.e. always on the highest Uclamp >> constraint? >> >> #define for_each_clamp_id(clamp_id) \ >> for ((clamp_id) = 0; (clamp_id) < UCLAMP_CNT; (clamp_id)++) >> >> In this case the code change can be as easy as in your original v3. >> >> Setting UCLAMP_FLAG_IDLE in uclamp_idle_value(): >> >> uclamp_rq_dec_id() -> uclamp_rq_max_value() -> *uclamp_idle_value()* >> >> Resetting UCLAMP_FLAG_IDLE in uclamp_idle_reset(): >> >> uclamp_rq_inc_id() -> *uclamp_idle_reset()* >> >> This would be more symmetrical then uclamp_idle_value() and >> uclamp_rq_inc()/uclamp_rq_reinc_id(). > > Right, thanks for the suggestion but to be fair I feel like this is a > matter of personal preference at this point. I personally like the way > it is in this patch -- I find it easier to reason about, but maybe > that's because I wrote it ... > > Do you feel strongly about it? If not I'd prefer to not re-spin this > another time if possible. Let me know what you think. No, not at all ;-) Just like it better since it would mean less code changes and only one place to reset UCLAMP_FLAG_IDLE. You can add a: Tested-by: Dietmar Eggemann to your version in case you want to keep it.