Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755743Ab2BFVTq (ORCPT ); Mon, 6 Feb 2012 16:19:46 -0500 Received: from mail-gx0-f174.google.com ([209.85.161.174]:59832 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755308Ab2BFVTp convert rfc822-to-8bit (ORCPT ); Mon, 6 Feb 2012 16:19:45 -0500 MIME-Version: 1.0 In-Reply-To: <20120206203738.GB556@aftab> References: <20120206132546.GA30854@quad> <1328538403.2482.4.camel@laptop> <20120206153408.GA31237@aftab> <1328546246.2482.10.camel@laptop> <20120206164626.GA31704@aftab> <1328547259.2482.11.camel@laptop> <20120206202722.GA556@aftab> <1328560293.2482.24.camel@laptop> <20120206203738.GB556@aftab> Date: Mon, 6 Feb 2012 13:19:44 -0800 Message-ID: Subject: Re: [BUG] perf: perf sched warning possibly due to clock granularity on AMD From: Venki Pallipadi To: Borislav Petkov Cc: Peter Zijlstra , Stephane Eranian , linux-kernel@vger.kernel.org, acme@redhat.com, mingo@elte.hu, robert.richter@amd.com, eric.dumazet@gmail.com, Andreas Herrmann X-System-Of-Record: true Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2423 Lines: 59 On Mon, Feb 6, 2012 at 12:37 PM, Borislav Petkov wrote: > On Mon, Feb 06, 2012 at 09:31:33PM +0100, Peter Zijlstra wrote: >> On Mon, 2012-02-06 at 21:27 +0100, Borislav Petkov wrote: >> > On Mon, Feb 06, 2012 at 05:54:19PM +0100, Peter Zijlstra wrote: >> > > On Mon, 2012-02-06 at 17:46 +0100, Borislav Petkov wrote: >> > > > > across all CPUs in the entire system. >> > > > >> > > > Right, by the "entire system" you mean consistent across cores and >> > > > sockets but not necessarily across cabinets, as in the comment above, >> > > > correct? >> > > > >> > > > If so, let me ask around if this holds true too. >> > > >> > > Every CPU available to the kernel. So if you run a single system image >> > > across your cabinets, then yes those too. >> > >> > Ok, but what about that sentence "(but not across cabinets - we turn >> > it off in that case explicitly.)" - I don't see any place where it is >> > turned off explicitly... Maybe a stale comment? >> >> I suspect it might be the sched_clock_stable = 0 in mark_tsc_unstable(), >> but lets ask Venki, IIRC he wrote all that. > > Yeah, I was looking at the code further and on Intel it does: > > ? ? ? ?if (c->x86_power & (1 << 8)) { > ? ? ? ? ? ? ? ?set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); > ? ? ? ? ? ? ? ?set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC); > ? ? ? ? ? ? ? ?if (!check_tsc_unstable()) > ? ? ? ? ? ? ? ? ? ? ? ?sched_clock_stable = 1; > ? ? ? ?} > > while on AMD, in early_init_amd() we do: > > ? ? ? ?if (c->x86_power & (1 << 8)) { > ? ? ? ? ? ? ? ?set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); > ? ? ? ? ? ? ? ?set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC); > ? ? ? ?} > > and having in mind that tsc_unstable is set on generic x86 paths, > nothing stops us to do the same on AMD too, and as a result, set > sched_clock_stable too. > > But yeah, let's see what Venki has to say first. > Looks like cabinet comment came from Ingo (commit 83ce4009) in reference to (We will turn this off in DMI quirks for multi-chassis systems) Yes. If these two flags are set, TSC should be consistent and sched_clock_stable could be set and it will be reset if there is a call to mark_tsc_unstable(). Thanks, Venki -- 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/