From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753499AbdHPAjj (ORCPT ); Tue, 15 Aug 2017 20:39:39 -0400 Received: from LGEAMRELO12.lge.com ([156.147.23.52]:48878 "EHLO lgeamrelo12.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752859AbdHPAjh (ORCPT ); Tue, 15 Aug 2017 20:39:37 -0400 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Wed, 16 Aug 2017 09:38:11 +0900 From: Byungchul Park To: Steven Rostedt Cc: peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org, juri.lelli@gmail.com, kernel-team@lge.com Subject: Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Message-ID: <20170816003810.GO20323@X58A-UD3R> References: <1502077834-11137-1-git-send-email-byungchul.park@lge.com> <1502077834-11137-2-git-send-email-byungchul.park@lge.com> <20170815111940.07c7f3de@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170815111940.07c7f3de@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 15, 2017 at 11:19:40AM -0400, Steven Rostedt wrote: > > @@ -1385,6 +1407,17 @@ static int find_later_rq(struct task_struct *task) > > * already under consideration through later_mask. > > */ > > if (best_cpu < nr_cpu_ids) { > > + /* > > + * If current domain is SD_PREFER_SIBLING > > + * flaged, we have to get more chances to > > + * check other siblings. > > + */ > > + if (sd->flags & SD_PREFER_SIBLING) { > > + prefer = sd; > > Is this how the SD_PREFER_SIBLING works? According to this, the > preferred sd is the next sd in for_each_domain(). Not to mention, the > prefer variable stays set if the next domain has no available CPUs. Is > that what we want? Maybe I don't understand what you want to say. The variable, prefer, is used to pick up the smallest sched domain among SD_PREFER_SIBLING domains, if more than one SD_PREFER_SIBLING domain exist in the visit. The prefer variable alway points to the previous SD_PREFER_SIBLING domain. And that must stay set to be used as a fallback choise if the next domain has no available CPUs. Could you explain what I mis-understand? Thanks, Byungchul > -- Steve > > > > + if (fallback_cpu == -1) > > + fallback_cpu = best_cpu; > > + continue; > > + } > > rcu_read_unlock(); > > return best_cpu; > > } > > @@ -1393,6 +1426,13 @@ static int find_later_rq(struct task_struct *task) > > rcu_read_unlock(); > > > > /* > > + * If fallback_cpu is valid, all our guesses failed *except* for > > + * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu. > > + */ > > + if (fallback_cpu != -1) > > + return fallback_cpu; > > + > > + /* > > * At this point, all our guesses failed, we just return > > * 'something', and let the caller sort the things out. > > */