Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759484AbZDAMoc (ORCPT ); Wed, 1 Apr 2009 08:44:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759482AbZDAMoR (ORCPT ); Wed, 1 Apr 2009 08:44:17 -0400 Received: from mga11.intel.com ([192.55.52.93]:49244 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757933AbZDAMoQ convert rfc822-to-8bit (ORCPT ); Wed, 1 Apr 2009 08:44:16 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.39,306,1235980800"; d="scan'208";a="677803480" From: "Metzger, Markus T" To: Ingo Molnar , Oleg Nesterov , Peter Zijlstra CC: "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "hpa@zytor.com" , "markus.t.metzger@gmail.com" , "roland@redhat.com" , "eranian@googlemail.com" , "Villacis, Juan" , "ak@linux.jf.intel.com" Date: Wed, 1 Apr 2009 13:43:26 +0100 Subject: RE: [patch 3/21] x86, bts: wait until traced task has been scheduled out Thread-Topic: [patch 3/21] x86, bts: wait until traced task has been scheduled out Thread-Index: Acmyvt0R+xcMM6pLSXOryf87tbkbLgACClaA Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E926D537D@irsmsx504.ger.corp.intel.com> References: <20090331145947.A12565@sedona.ch.intel.com> <20090401001729.GC28228@redhat.com> <20090401114140.GB23678@elte.hu> In-Reply-To: <20090401114140.GB23678@elte.hu> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2238 Lines: 75 >-----Original Message----- >From: Ingo Molnar [mailto:mingo@elte.hu] >Sent: Wednesday, April 01, 2009 1:42 PM >To: Oleg Nesterov; Peter Zijlstra >* Oleg Nesterov wrote: > >> On 03/31, Markus Metzger wrote: >> > >> > +static void wait_to_unschedule(struct task_struct *task) >> > +{ >> > + unsigned long nvcsw; >> > + unsigned long nivcsw; >> > + >> > + if (!task) >> > + return; >> > + >> > + if (task == current) >> > + return; >> > + >> > + nvcsw = task->nvcsw; >> > + nivcsw = task->nivcsw; >> > + for (;;) { >> > + if (!task_is_running(task)) >> > + break; >> > + /* >> > + * The switch count is incremented before the actual >> > + * context switch. We thus wait for two switches to be >> > + * sure at least one completed. >> > + */ >> > + if ((task->nvcsw - nvcsw) > 1) >> > + break; >> > + if ((task->nivcsw - nivcsw) > 1) >> > + break; >> > + >> > + schedule(); >> >> schedule() is a nop here. We can wait unpredictably long... >> >> Ingo, do have have any ideas to improve this helper? > >hm, there's a similar looking existing facility: >wait_task_inactive(). Have i missed some subtle detail that makes it >inappropriate for use here? wait_task_inactive() waits until the task is no longer TASK_RUNNING. I need to wait until the task has been scheduled out at least once. regards, markus. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -- 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/