From: Andi Kleen <ak@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org, Jiri Olsa <jolsa@redhat.com>,
Stephane Eranian <eranian@google.com>,
mathieu.poirier@linaro.org, Pawel Moll <pawel.moll@arm.com>
Subject: Re: [RFC PATCH] perf: Add PERF_RECORD_SWITCH to indicate context switches
Date: Thu, 11 Jun 2015 09:34:30 -0700 [thread overview]
Message-ID: <20150611163430.GC25760@tassilo.jf.intel.com> (raw)
In-Reply-To: <20150611141548.GW19282@twins.programming.kicks-ass.net>
On Thu, Jun 11, 2015 at 04:15:48PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 09, 2015 at 05:21:10PM +0300, Adrian Hunter wrote:
> > Tracepoints are no good at all for non-privileged users
> > because they need either CAP_SYS_ADMIN or
> > /proc/sys/kernel/perf_event_paranoid <= -1.
> >
> > On the other hand, kernel software events need either
> > CAP_SYS_ADMIN or /proc/sys/kernel/perf_event_paranoid <= 1.
>
> So while I think it makes sense to allow some tracepoint outside of that
> priv level, IOW have a per tracepoint priv level filter thingy, I don't
> think sched_switch() is one of those because it explicitly exposes
> timing information on other tasks.
It's trivial for a running program to measure when it gets context switched
by looking at timing. I don't think this event provides anything new over that.
-Andi
next prev parent reply other threads:[~2015-06-11 16:34 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-09 14:21 [RFC PATCH] perf: Add PERF_RECORD_SWITCH to indicate context switches Adrian Hunter
2015-06-11 14:15 ` Peter Zijlstra
2015-06-11 16:34 ` Andi Kleen [this message]
2015-06-11 16:54 ` Peter Zijlstra
2015-06-12 0:47 ` David Ahern
2015-06-12 10:34 ` Adrian Hunter
2015-06-12 14:21 ` David Ahern
2015-06-12 16:13 ` Adrian Hunter
2015-06-12 11:12 ` Adrian Hunter
2015-06-12 12:09 ` Peter Zijlstra
2015-06-12 12:36 ` Arnaldo Carvalho de Melo
2015-06-12 13:15 ` Adrian Hunter
2015-06-12 13:28 ` Pawel Moll
2015-06-12 13:52 ` Pawel Moll
2015-06-12 14:30 ` David Ahern
2015-06-12 14:29 ` David Ahern
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