Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754808AbbHCRjm (ORCPT ); Mon, 3 Aug 2015 13:39:42 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:36404 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751194AbbHCRjl (ORCPT ); Mon, 3 Aug 2015 13:39:41 -0400 Date: Mon, 3 Aug 2015 19:39:37 +0200 From: Frederic Weisbecker To: Peter Zijlstra Cc: Chris Metcalf , LKML , Thomas Gleixner , Preeti U Murthy , Christoph Lameter , Ingo Molnar , Viresh Kumar , Rik van Riel Subject: Re: [PATCH 08/10] posix-cpu-timers: Migrate to use new tick dependency mask model Message-ID: <20150803173936.GC26022@lerouge> References: <1437669735-8786-9-git-send-email-fweisbec@gmail.com> <55B26E74.5040803@ezchip.com> <20150729132343.GC11554@lerouge> <55B90C40.5090000@ezchip.com> <20150730004444.GA14744@lerouge> <55BA7C6A.1050602@ezchip.com> <20150730194519.GA24607@lerouge> <55BA8096.7030601@ezchip.com> <20150731144954.GB27875@lerouge> <20150803171243.GW25159@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150803171243.GW25159@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1227 Lines: 24 On Mon, Aug 03, 2015 at 07:12:43PM +0200, Peter Zijlstra wrote: > On Fri, Jul 31, 2015 at 04:49:55PM +0200, Frederic Weisbecker wrote: > > Instead of doing a per signal dependency, I'm going to use a per task > > one. > > Urgh, does this mean you'll keep the horrid tick_nohz_task_switch() > thing? I thought I would drop it, but now that I think about it more, I think I need to keep it because if we enqueue a posix timer to a sleeping task and that task later wakes up, we must restart the tick, and that is only possible with a check on context switch :-( This current patchset removed the need for that with a global dependency for posix timers: as long as there is one enqueued we keep the tick. But Chris and Luiz fear that Tilera users have posix timers on housekeepers. They also suggested we offline the posix timers. I fear it's going to be a high overhead as it means polling on the target task context of execution. Unless we move the task itself to housekeepers... -- 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/