From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752264Ab3F0M2b (ORCPT ); Thu, 27 Jun 2013 08:28:31 -0400 Received: from moutng.kundenserver.de ([212.227.17.10]:61871 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751566Ab3F0M2a (ORCPT ); Thu, 27 Jun 2013 08:28:30 -0400 Message-ID: <1372336081.5871.168.camel@marge.simpson.net> Subject: Re: deadlock in scheduler enabling HRTICK feature From: Mike Galbraith To: Peter Zijlstra Cc: David Ahern , Ingo Molnar , LKML , tglx@linutronix.de Date: Thu, 27 Jun 2013 14:28:01 +0200 In-Reply-To: <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> <20130627105303.GD27378@dyad.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Provags-ID: V02:K0:/+wJpMFhpTDBQiTMH353HefAmH6G2cYMghjcXXzzVUD ZjX/yPxC5iOvF1rs5W3axhI+R6KwuXClZlf8xi5/N0zNzWnCZt UR1DLiyEQzAiypipY57fcxWL7N9ynrg8BUzPSrjQLPuXyVlJy1 hXW1fncDyzkM8JKpRh2mfE7KRA/yVM2TKwm8Kr70sEkbNg7lBz qTOVG3GVnO5vM0M/YIGAvtEDMsclP1EGOWzNCfn3F4HHnHjLPU znloNWyaodUhQiI4dddUht8EIPp51nXVQ1YKs0Nvq8cY9UqkDd oUdESoC3pgCOKNude9oR4VfEkcwrUwkYU6mvMpKw5j1yfSw7GL 9NN9QdmJ4fqU0PVAxP34HE5xCecWTzjJDUDjb0ZnFdYuVB1TnS 7fuHoQRGb4mKg== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2013-06-27 at 12:53 +0200, 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. That cost sprang to mind when you mentioned that deadline needs hrtick. > 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. Could be worse, flaming marshmallows stick. -Mike