From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753617AbbBJJDt (ORCPT ); Tue, 10 Feb 2015 04:03:49 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:39620 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751032AbbBJJDo (ORCPT ); Tue, 10 Feb 2015 04:03:44 -0500 Date: Tue, 10 Feb 2015 10:03:36 +0100 From: Peter Zijlstra To: Jason Baron Cc: mingo@redhat.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, normalperson@yhbt.net, davidel@xmailserver.org, mtk.manpages@gmail.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 1/2] sched/wait: add round robin wakeup mode Message-ID: <20150210090336.GV21418@twins.programming.kicks-ass.net> References: <20150209215045.GU21418@twins.programming.kicks-ass.net> <54D983B9.800@akamai.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54D983B9.800@akamai.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 09, 2015 at 11:06:17PM -0500, Jason Baron wrote: > On 02/09/2015 04:50 PM, Peter Zijlstra wrote: > > On Mon, Feb 09, 2015 at 08:05:57PM +0000, Jason Baron wrote: > >> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c > >> index 852143a..17d1039 100644 > >> --- a/kernel/sched/wait.c > >> +++ b/kernel/sched/wait.c > >> @@ -71,8 +71,11 @@ static void __wake_up_common(wait_queue_head_t *q, unsigned int mode, > >> unsigned flags = curr->flags; > >> > >> if (curr->func(curr, mode, wake_flags, key) && > >> - (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) > >> + (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) { > >> + if (flags & WQ_FLAG_ROUND_ROBIN) > >> + list_move_tail(&curr->task_list, &q->task_list); > >> break; > >> + } > >> } > >> } > > I think you meant to write something like: > > > > if (curr->func(curr, mode, wake_flags, key) && > > (flags & WQ_FLAG_EXCLUSIVE)) { > > if (flag & WQ_FLAG_ROUND_ROBIN) > > list_move_tail(&curr->task_list, &q->task_list); > > if (!--nr_exclusive) > > break; > > } > > > > Otherwise can only work for nr_exclusive==1. > > Indeed. I'm also wondering if its worth avoiding the list_move_tail() > for the case where nr_exclusive is initially 0. IE the wake all case, > where we are just going to end up doing a bunch of list_move_tail() > calls, but end up in the same state. After writing this email, it occurred to me that you could probably do this with a custom wake function. Where autoremove_wake_function() does a list_del_init() you could do a rotate_wake_function() that does list_move_tail(). That would avoid the entire WQ flag muckery.