From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752154Ab2LQJoM (ORCPT ); Mon, 17 Dec 2012 04:44:12 -0500 Received: from mail-wi0-f180.google.com ([209.85.212.180]:39806 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751213Ab2LQJoL (ORCPT ); Mon, 17 Dec 2012 04:44:11 -0500 Date: Mon, 17 Dec 2012 10:44:03 +0100 From: Robert Richter To: Ingo Molnar Cc: suravee.suthikulpanit@amd.com, a.p.zijlstra@chello.nl, paulus@samba.org, mingo@redhat.com, acme@ghostprotocols.net, tglx@linutronix.de, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org, jacob.shin@amd.com Subject: Re: [PATCH 1/1] Change IBS PMU to use perf_hw_context Message-ID: <20121217094403.GF1893@rric.localhost> References: <1355518662-32071-1-git-send-email-suravee.suthikulpanit@amd.com> <20121216090410.GC21690@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121216090410.GC21690@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16.12.12 10:04:10, Ingo Molnar wrote: > > * suravee.suthikulpanit@amd.com wrote: > > > From: Suravee Suthikulpanit > > > > Currently, the AMD IBS PMU initialize pmu.task_ctx_nr to > > perf_invalid_context which only allows IBS to be running only > > in system-wide mode (e.g. perf record -a). IBS hardware is > > available in each core and should be per-context. This patch > > modifies the task_ctx_nr to use the perf_hw_context (default) > > instead. > > I'm wondering how extensively was it tested/verified that it's > safe to enable IBS in per context mode as well, and that the > profiling results are precise and accurate? >>From the implementation's point of view this is very similar to hw perf counters. I wouldn't expect any issues here. Since IBS can be immediatly started/stopped and there is no caching, there won't be any incomming sample that is not related to that context. The only potential problem I see could be a security risk in a way that an IBS sample might expose data related to other contexts such as cache information. This is similar to uncore/northbridge events so I don't think this is an issue, but we might want to evaluate this. > We never used the IBS hardware in this fashion before, so some > extra care is prudent - and traces of that extra care should be > visible in the changelog as well. Yeah, a comparison of numbers for IBS and hw counter (-e r076:p,r076 and -e r0C1:p,r0C1) in per-context mode would be useful here. -Robert