From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752453Ab3F0Kxc (ORCPT ); Thu, 27 Jun 2013 06:53:32 -0400 Received: from merlin.infradead.org ([205.233.59.134]:53844 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751319Ab3F0Kxb (ORCPT ); Thu, 27 Jun 2013 06:53:31 -0400 Date: Thu, 27 Jun 2013 12:53:03 +0200 From: Peter Zijlstra To: David Ahern Cc: Ingo Molnar , LKML , tglx@linutronix.de Subject: Re: deadlock in scheduler enabling HRTICK feature Message-ID: <20130627105303.GD27378@dyad.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130627104309.GQ28407@twins.programming.kicks-ass.net> 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 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. 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.