Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758587AbZFBHZ2 (ORCPT ); Tue, 2 Jun 2009 03:25:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756987AbZFBHZU (ORCPT ); Tue, 2 Jun 2009 03:25:20 -0400 Received: from casper.infradead.org ([85.118.1.10]:45230 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754706AbZFBHZT (ORCPT ); Tue, 2 Jun 2009 03:25:19 -0400 Subject: Re: [PATCH] sched: sched_clock() clocksource handling. From: Peter Zijlstra To: Paul Mundt Cc: Ingo Molnar , Thomas Gleixner , Daniel Walker , Linus Walleij , Andrew Victor , Haavard Skinnemoen , Andrew Morton , John Stultz , linux-arm-kernel@lists.arm.linux.org.uk, linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20090602071718.GA17710@linux-sh.org> References: <20090602071718.GA17710@linux-sh.org> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Tue, 02 Jun 2009 09:25:02 +0200 Message-Id: <1243927502.23657.5619.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1579 Lines: 51 On Tue, 2009-06-02 at 16:17 +0900, Paul Mundt wrote: > @@ -362,6 +364,9 @@ static struct clocksource *select_clocksource(void) > if (next == curr_clocksource) > return NULL; > > + if (next->flags & CLOCK_SOURCE_USE_FOR_SCHED_CLOCK) > + sched_clocksource = next; > + > return next; > } > > @@ -440,7 +445,21 @@ void clocksource_unregister(struct clocksource *cs) > list_del(&cs->list); > if (clocksource_override == cs) > clocksource_override = NULL; > + > next_clocksource = select_clocksource(); > + > + /* > + * If select_clocksource() fails to find another suitable > + * clocksource for sched_clocksource and we are unregistering > + * it, switch back to jiffies. > + */ > + if (sched_clocksource == cs) { > + rcu_assign_pointer(sched_clocksource, &clocksource_jiffies); > + spin_unlock_irqrestore(&clocksource_lock, flags); > + synchronize_rcu(); > + return; > + } > + > spin_unlock_irqrestore(&clocksource_lock, flags); > } What if there's multiple CLOCK_SOURCE_USER_FOR_SCHED_CLOCK [ damn, thats a long name to type :-) ] ? That is, should we have logic in select_clocksource that does: if ((next->flags & ..) && next->prio > sched_clocksource->prio) or whatever, so that it picks the best one? Same for unregister, should we re-evaluate all clocksources before falling back to basic? -- 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/