From patchwork Thu May 17 13:07:04 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joel Fernandes X-Patchwork-Id: 10406783 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 260F560155 for ; Thu, 17 May 2018 13:07:12 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 135D82818E for ; Thu, 17 May 2018 13:07:12 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 074D828A7C; Thu, 17 May 2018 13:07:12 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 64DB92818E for ; Thu, 17 May 2018 13:07:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752393AbeEQNHJ (ORCPT ); Thu, 17 May 2018 09:07:09 -0400 Received: from mail-pl0-f66.google.com ([209.85.160.66]:36328 "EHLO mail-pl0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751965AbeEQNHG (ORCPT ); Thu, 17 May 2018 09:07:06 -0400 Received: by mail-pl0-f66.google.com with SMTP id v24-v6so2527533plo.3 for ; Thu, 17 May 2018 06:07:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=yWPDJTWIj4bCPGKze+tB+RHlIbS/s2BthLLfpjiikac=; b=WcaQf6krIuiuQr1WEYqax0UqRZDxpt9Xzzot27IYryUSQk6l/oMw60TyLZgMQUjDY1 77gkQNiAYYsXyCkHuXNFxY//w36+q+dHDHgpFhIMltiimrrVM8r6ssswWMHAj6kPHn4W YFs7RX08/HaNcMIJCc5lPf2jpa4blRpG7GW04= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=yWPDJTWIj4bCPGKze+tB+RHlIbS/s2BthLLfpjiikac=; b=KK04HQc6jAoSry3iikvWswE650Sk5AYV1pQuG8Yh6UAkH1AikvhHTiyLva0NqnMP97 WS9PNOFuxqglrDvlExZzmFBenIuHwpQalotZvc41Bd65ncrsK6bqB+NeWThEJQmFSazp 0PMSvZiC/+FCHejS1DzV32kY//7bcj77ePb9p+zXRdkh6qdLK65JTFo9Lcz1TQvE7Z3S 4ptjfrCWBMe6jGmPSCLUEmSIQWI8NY2WNfJsGb/UKVqDqeTMREs5S+OJVN87ibjpLFbC ahZ82qMu12WewWZgmwx2mCwddQilOXXiRlSeKWf9J9lHwsekjaKov7YyaFFjTzdAPXlR 3eRQ== X-Gm-Message-State: ALKqPwcfsP1HuHJtr83Ea7qnaMO2qiOvV7w28mb9t9rDgBnxu+SFXGcu VdFFsoHJctJEiWcBhhUI9gIllw== X-Google-Smtp-Source: AB8JxZoEPO4dozeueMH3FbAjrTvqLOElSf2ldkRHZMi6NG7gEl8Qb9XwfK0Zf64tJDQQewmv6nAvHg== X-Received: by 2002:a17:902:9a8b:: with SMTP id w11-v6mr5163841plp.75.1526562425862; Thu, 17 May 2018 06:07:05 -0700 (PDT) Received: from localhost ([2620:0:1000:1600:3122:ea9c:d178:eb]) by smtp.gmail.com with ESMTPSA id f2-v6sm2621516pgp.28.2018.05.17.06.07.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 17 May 2018 06:07:05 -0700 (PDT) Date: Thu, 17 May 2018 06:07:04 -0700 From: Joel Fernandes To: Juri Lelli Cc: Viresh Kumar , linux-kernel@vger.kernel.org, "Rafael J . Wysocki" , Peter Zijlstra , Ingo Molnar , Patrick Bellasi , Luca Abeni , Joel Fernandes , linux-pm@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH RFC] schedutil: Allow cpufreq requests to be made even when kthread kicked Message-ID: <20180517130704.GA139147@joelaf.mtv.corp.google.com> References: <20180516224518.109891-1-joel@joelfernandes.org> <20180517070026.GA22493@localhost.localdomain> <20180517102024.s3dxo4uepujh5f65@vireshk-i7> <20180517105358.GB22493@localhost.localdomain> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20180517105358.GB22493@localhost.localdomain> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On Thu, May 17, 2018 at 12:53:58PM +0200, Juri Lelli wrote: > On 17/05/18 15:50, Viresh Kumar wrote: > > On 17-05-18, 09:00, Juri Lelli wrote: > > > Hi Joel, > > > > > > On 16/05/18 15:45, Joel Fernandes (Google) wrote: > > > > > > [...] > > > > > > > @@ -382,13 +391,24 @@ sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags) > > > > static void sugov_work(struct kthread_work *work) > > > > { > > > > struct sugov_policy *sg_policy = container_of(work, struct sugov_policy, work); > > > > + unsigned int freq; > > > > + unsigned long flags; > > > > + > > > > + /* > > > > + * Hold sg_policy->update_lock shortly to handle the case where: > > > > + * incase sg_policy->next_freq is read here, and then updated by > > > > + * sugov_update_shared just before work_in_progress is set to false > > > > + * here, we may miss queueing the new update. > > > > + */ > > > > + raw_spin_lock_irqsave(&sg_policy->update_lock, flags); > > > > + freq = sg_policy->next_freq; > > > > + sg_policy->work_in_progress = false; > > > > + raw_spin_unlock_irqrestore(&sg_policy->update_lock, flags); > > > > > > OK, we queue the new request up, but still we need to let this kthread > > > activation complete and then wake it up again to service the request > > > already queued, right? Wasn't what Claudio proposed (service back to > > > back requests all in the same kthread activation) better from an > > > overhead pow? Hmm, from that perspective, yeah. But note that my patch doesn't increase the overhead from what it already is.. because we don't queue the irq_work again unless work_in_progress is cleared, which wouldn't be if the kthread didn't run yet. > > > > We would need more locking stuff in the work handler in that case and > > I think there maybe a chance of missing the request in that solution > > if the request happens right at the end of when sugov_work returns. > > Mmm, true. Ideally we might want to use some sort of queue where to > atomically insert requests and then consume until queue is empty from > sugov kthread. IMO we don't really need a queue or anything, we should need the kthread to process the *latest* request it sees since that's the only one that matters. > But, I guess that's going to be too much complexity for an (hopefully) > corner case. I thought of this corner case too, I'd argue its still an improvement over not doing anything, but we could tighten this up a bit more if you wanted by doing something like this on top of my patch. Thoughts? ---8<----------------------- diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index a87fc281893d..e45ec24b810b 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -394,6 +394,7 @@ static void sugov_work(struct kthread_work *work) unsigned int freq; unsigned long flags; +redo_work: /* * Hold sg_policy->update_lock shortly to handle the case where: * incase sg_policy->next_freq is read here, and then updated by @@ -409,6 +410,9 @@ static void sugov_work(struct kthread_work *work) __cpufreq_driver_target(sg_policy->policy, freq, CPUFREQ_RELATION_L); mutex_unlock(&sg_policy->work_lock); + + if (sg_policy->work_in_progress) + goto redo_work; } static void sugov_irq_work(struct irq_work *irq_work)