From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753556AbdHPCTA (ORCPT ); Tue, 15 Aug 2017 22:19:00 -0400 Received: from LGEAMRELO12.lge.com ([156.147.23.52]:33445 "EHLO lgeamrelo12.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753012AbdHPCS7 (ORCPT ); Tue, 15 Aug 2017 22:18:59 -0400 X-Original-SENDERIP: 156.147.1.121 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 11:17:36 +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: <20170816021736.GP20323@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> <20170816003810.GO20323@X58A-UD3R> <20170815214201.15b6424b@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170815214201.15b6424b@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 09:42:01PM -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. > > BTW, "we have to get more chances" doesn't really make sense. Do you > mean "we need to try other domains"? Yes, we need to try other domains first if current domain is SD_PREFER_SIBLING flaged. > > > > + */ > > > > + 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? > > > > I may be the one confused here ;-) > > I think I misread the patch. So, the SD_PREFER_SIBLING means to try to > find a CPU in another sd instead? Thus, we try to find a CPU in a sd > that does not have SD_PREFER_SIBLING set. And if there is none, we use > the preferred sd as a fallback. Is that correct? Yes, that's what I intended. IOW: If (we found a proper sd, not having SD_PREFER_SIBLING?) use the sd; else if (we found a proper sd, having SD_PREFER_SIBLING?) use the smallest sd among SD_PREFER_SIBLING sds; Thanks, Byungchul