From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754046AbcKIN7e (ORCPT ); Wed, 9 Nov 2016 08:59:34 -0500 Received: from mail.kernel.org ([198.145.29.136]:54192 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752802AbcKIN7d (ORCPT ); Wed, 9 Nov 2016 08:59:33 -0500 Date: Wed, 9 Nov 2016 10:59:27 -0300 From: Arnaldo Carvalho de Melo To: Arnaldo Carvalho de Melo Cc: Andi Kleen , linux-kernel@vger.kernel.org, Andi Kleen , adrian.hunter@intel.com Subject: Re: [PATCH] perf tools pt: Remove obsolete paragraph in intel-pt.c Message-ID: <20161109135927.GE12125@kernel.org> References: <1478650260-30140-1-git-send-email-andi@firstfloor.org> <20161109131426.GD12125@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161109131426.GD12125@kernel.org> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Wed, Nov 09, 2016 at 10:14:26AM -0300, Arnaldo Carvalho de Melo escreveu: > Em Tue, Nov 08, 2016 at 04:11:00PM -0800, Andi Kleen escreveu: > > From: Andi Kleen > > > > Since the unprivileged sched switch event was added in perf, > > PT doesn't need need perf_event_paranoid=-1 anymore for > > per cpu decoding. So remove the obsolete paragraph in > > the documentation. > > Thanks for pointing that out, I'll do something slightly different tho, > pointing out that from kernel X.Y.Z, when the unprivileged > PERF_RECORD_SWITCH metadata event was introduced, this is no longer an > issue, having to be considered only on older kernels. It ended up as: diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt index c6c8318e38a2..4d12db118476 100644 --- a/tools/perf/Documentation/intel-pt.txt +++ b/tools/perf/Documentation/intel-pt.txt @@ -546,6 +546,18 @@ mode by using the --per-thread option. Privileged vs non-privileged users ---------------------------------- +The v4.2 kernel introduced support for a context switch metadata event, +PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes +are scheduled out and in, just not by whom, which is left for the +PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context, +which in turn requires CAP_SYS_ADMIN. + +Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context +switches") commit, that introduces these metadata events for further info. + +When working with kernels < v4.2, the following considerations must be taken, +as the sched:sched_switch tracepoints will be used to receive such information: + Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users have memory limits imposed upon them. That affects what buffer sizes they can have as outlined above.