From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932648AbcKIOGP (ORCPT ); Wed, 9 Nov 2016 09:06:15 -0500 Received: from mga04.intel.com ([192.55.52.120]:55805 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932217AbcKIOGP (ORCPT ); Wed, 9 Nov 2016 09:06:15 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.31,614,1473145200"; d="scan'208";a="1082831689" Subject: Re: [PATCH] perf tools pt: Remove obsolete paragraph in intel-pt.c To: Arnaldo Carvalho de Melo , Arnaldo Carvalho de Melo References: <1478650260-30140-1-git-send-email-andi@firstfloor.org> <20161109131426.GD12125@kernel.org> <20161109135927.GE12125@kernel.org> Cc: Andi Kleen , linux-kernel@vger.kernel.org, Andi Kleen From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki Message-ID: <344fddd4-718b-ecf3-75f0-585eda90df6f@intel.com> Date: Wed, 9 Nov 2016 16:01:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20161109135927.GE12125@kernel.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/11/16 15:59, Arnaldo Carvalho de Melo wrote: > 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. Maybe put that last paragraph about memory limits above the new text.