Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759978Ab3D2VwG (ORCPT ); Mon, 29 Apr 2013 17:52:06 -0400 Received: from mail-pd0-f181.google.com ([209.85.192.181]:52190 "EHLO mail-pd0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758406Ab3D2VwD (ORCPT ); Mon, 29 Apr 2013 17:52:03 -0400 Date: Mon, 29 Apr 2013 14:51:57 -0700 From: Tejun Heo To: Colin Cross Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, "Rafael J. Wysocki" , arve@android.com, Li Zefan , Len Brown , Pavel Machek , containers@lists.linux-foundation.org, cgroups@vger.kernel.org Subject: Re: [PATCH 02/10] freezer: skip waking up tasks with PF_FREEZER_SKIP set Message-ID: <20130429215157.GA2395@htj.dyndns.org> References: <1367271946-7239-1-git-send-email-ccross@android.com> <1367271946-7239-3-git-send-email-ccross@android.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1367271946-7239-3-git-send-email-ccross@android.com> 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 Content-Length: 1651 Lines: 46 Hello, On Mon, Apr 29, 2013 at 02:45:38PM -0700, Colin Cross wrote: > If a task has called freezer_do_not_count(), don't bother waking it > up. If it happens to wake up later it will call freezer_count() and > immediately enter the refrigerator. > > Signed-off-by: Colin Cross > --- > kernel/cgroup_freezer.c | 5 ++++- > kernel/power/process.c | 4 ++-- > 2 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c > index 75dda1e..406dd71 100644 > --- a/kernel/cgroup_freezer.c > +++ b/kernel/cgroup_freezer.c > @@ -331,8 +331,11 @@ static void freeze_cgroup(struct freezer *freezer) > struct task_struct *task; > > cgroup_iter_start(cgroup, &it); > - while ((task = cgroup_iter_next(cgroup, &it))) > + while ((task = cgroup_iter_next(cgroup, &it))) { > + if (freezer_should_skip(task)) > + continue; > freeze_task(task); > + } > cgroup_iter_end(cgroup, &it); I feel a bit weary of changes which try to optimize state checks for freezer because the synchronization rules are kinda fragile and things may not work reliably depending on who's testing the flag, and it has been subtly broken in various ways in the past (maybe even now). Can you please explain the benefits of this patch (in terms of actual overhead because not many use freezer_do_not_count()) and why this is correct? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/