Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756245AbaGVQsJ (ORCPT ); Tue, 22 Jul 2014 12:48:09 -0400 Received: from fw-tnat.austin.arm.com ([217.140.110.23]:46863 "EHLO collaborate-mta1.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755885AbaGVQsG (ORCPT ); Tue, 22 Jul 2014 12:48:06 -0400 Message-ID: <1406047681.25343.79.camel@hornet> Subject: Re: [RFC] sched_clock: Track monotonic raw clock From: Pawel Moll To: Peter Zijlstra Cc: Richard Cochran , Steven Rostedt , Ingo Molnar , Oleg Nesterov , Andrew Morton , Mel Gorman , Andy Lutomirski , John Stultz , Stephen Boyd , Baruch Siach , Thomas Gleixner , "linux-kernel@vger.kernel.org" Date: Tue, 22 Jul 2014 17:48:01 +0100 In-Reply-To: <20140722163437.GI3935@laptop> References: <1405705419-4194-1-git-send-email-pawel.moll@arm.com> <20140719050233.GA4408@netboy> <1406045849.25343.72.camel@hornet> <20140722163437.GI3935@laptop> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-07-22 at 17:34 +0100, Peter Zijlstra wrote: > On Tue, Jul 22, 2014 at 05:17:29PM +0100, Pawel Moll wrote: > > With both Ingo and John showing preference towards the clock alignment, > > so that's where I looked this time (I've already done custom perf > > ioctls, posix clocks... don't really know how many different ways I've > > tried). > > So we should probably also talk about which clock to track, MONO has the > advantage of making it far easier to trace clusters but has the > disadvantage of stacked control loops with NTP adjusting MONO and us > adjusting sched_clock. John suggested (and I fully agree with him) MONO_RAW, as it is not getting NTP-d. > And I would really prefer to pick 1 and not make it configurable. Same here. One thing I keep in mind is the fact that userspace must be able to say whether it can expect the correlation or not. "Not" being either an architecture which sched_clock is not using the generic solution (I'm sure there will be some) or "not" because of the synchronisation failure. My idea so far was a debugfs file saying this (or missing, which is a message on its own). Pawel -- 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/