From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941342AbcKOBjf (ORCPT ); Mon, 14 Nov 2016 20:39:35 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:60441 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S941290AbcKOBj3 (ORCPT ); Mon, 14 Nov 2016 20:39:29 -0500 From: Arnaldo Carvalho de Melo To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, Arnaldo Carvalho de Melo Subject: [PATCH 02/15] perf intel-pt: Update documentation about context switch events Date: Mon, 14 Nov 2016 22:38:34 -0300 Message-Id: <1479173927-24613-3-git-send-email-acme@kernel.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1479173927-24613-1-git-send-email-acme@kernel.org> References: <1479173927-24613-1-git-send-email-acme@kernel.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arnaldo Carvalho de Melo Since the unprivileged sched switch event was added in perf, PT doesn't need need perf_event_paranoid=-1 anymore for per cpu decoding. Add a note stating that that is only needed for kernels < 4.2. Reported-by: Andi Kleen Report-Link: http://lkml.kernel.org/r/http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi42r@git.kernel.org Acked-by: Adrian Hunter Fixes: 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context switches") Link: http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi42r@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/Documentation/intel-pt.txt | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt index c6c8318e38a2..b0b3007d3c9c 100644 --- a/tools/perf/Documentation/intel-pt.txt +++ b/tools/perf/Documentation/intel-pt.txt @@ -550,6 +550,18 @@ 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. +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 are not permitted to use tracepoints which means there is insufficient side-band information to decode Intel PT in per-cpu mode, and potentially workload-only @@ -564,8 +576,11 @@ sched_switch tracepoint ----------------------- The sched_switch tracepoint is used to provide side-band data for Intel PT -decoding. sched_switch events are automatically added. e.g. the second event -shown below +decoding in kernels where the PERF_RECORD_SWITCH metadata event isn't +available. + +The sched_switch events are automatically added. e.g. the second event shown +below: $ perf record -vv -e intel_pt//u uname ------------------------------------------------------------ -- 2.7.4