Re: [RFC PATCH] perf: Add PERF_RECORD_SWITCH to indicate context switches

From: Andi Kleen
Date: Thu Jun 11 2015 - 12:34:38 EST


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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/