From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753997Ab3F0NGS (ORCPT ); Thu, 27 Jun 2013 09:06:18 -0400 Received: from mail-ee0-f44.google.com ([74.125.83.44]:54278 "EHLO mail-ee0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752902Ab3F0NGO (ORCPT ); Thu, 27 Jun 2013 09:06:14 -0400 Date: Thu, 27 Jun 2013 15:06:09 +0200 From: Ingo Molnar To: Peter Zijlstra Cc: David Ahern , LKML , tglx@linutronix.de Subject: Re: deadlock in scheduler enabling HRTICK feature Message-ID: <20130627130609.GA6655@gmail.com> References: <51CA0622.8010105@gmail.com> <20130625211713.GA18796@laptop.programming.kicks-ass.net> <51CA0980.8010409@gmail.com> <20130626070533.GA3601@dyad.programming.kicks-ass.net> <51CB1AE9.5090709@gmail.com> <20130627104309.GQ28407@twins.programming.kicks-ass.net> <20130627105303.GD27378@dyad.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130627105303.GD27378@dyad.programming.kicks-ass.net> 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 * Peter Zijlstra wrote: > On Thu, Jun 27, 2013 at 12:43:09PM +0200, Peter Zijlstra wrote: > > On Wed, Jun 26, 2013 at 10:46:33AM -0600, David Ahern wrote: > > > On 6/26/13 1:05 AM, Peter Zijlstra wrote: > > > >>What is the expectation that the feature provides? not a whole lot of > > > >>documentation on it. I walked down the path wondering if it solved an odd > > > >>problem we are seeing with the CFS in 2.6.27 kernel. > > > > > > > >Its supposed to use hrtimers for slice expiry instead of the regular tick. > > > > > > So theoretically CPU bound tasks would get preempted sooner? That was my > > > guess/hope anyways. > > > > Doth the below worketh? > > > > Related to all this; the reason its not enabled by default is that > mucking about with hrtimers all the while is god awful expensive. > > I've had ideas about making this a special purpose 'hard-coded' timer in > the hrtimer guts that's only ever re-programmed when the new value is > sooner. > > By making it a 'special' timer we can avoid the whole rb-tree song and > dance; and by taking 'spurious' short interrupts we can avoid prodding > the hardware too often. Sounds neat ... > Then again; Thomas will likely throw frozen seafood my way for even > proposing stuff like this and I'm not even sure that's going to be > enough to make the cost acceptable. (Could be worse: rotten seafood?) Thanks, Ingo