Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765662AbZDAAWV (ORCPT ); Tue, 31 Mar 2009 20:22:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763490AbZDAAVR (ORCPT ); Tue, 31 Mar 2009 20:21:17 -0400 Received: from mx2.redhat.com ([66.187.237.31]:56745 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1765471AbZDAAVQ (ORCPT ); Tue, 31 Mar 2009 20:21:16 -0400 Date: Wed, 1 Apr 2009 02:17:29 +0200 From: Oleg Nesterov To: Markus Metzger Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com, markus.t.metzger@gmail.com, roland@redhat.com, eranian@googlemail.com, juan.villacis@intel.com, ak@linux.jf.intel.com Subject: Re: [patch 3/21] x86, bts: wait until traced task has been scheduled out Message-ID: <20090401001729.GC28228@redhat.com> References: <20090331145947.A12565@sedona.ch.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090331145947.A12565@sedona.ch.intel.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2121 Lines: 91 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? Not that I really like it, but how about int force_unschedule(struct task_struct *p) { struct rq *rq; unsigned long flags; int running; rq = task_rq_lock(p, &flags); running = task_running(rq, p); task_rq_unlock(rq, &flags); if (running) wake_up_process(rq->migration_thread); return running; } which should be used instead of task_is_running() ? We can even do something like void wait_to_unschedule(struct task_struct *task) { struct migration_req req; rq = task_rq_lock(p, &task); running = task_running(rq, p); if (running) { // make sure __migrate_task() will do nothing req->dest_cpu = NR_CPUS + 1; init_completion(&req->done); list_add(&req->list, &rq->migration_queue); } task_rq_unlock(rq, &flags); if (running) { wake_up_process(rq->migration_thread); wait_for_completion(&req.done); } } This way we don't poll, and we need only one helper. (Can't resist, this patch is not bisect friendly, without the next patches wait_to_unschedule() is called under write_lock_irq, this is deadlockable). But anyway, I think we can do this later. Oleg. -- 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/