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

[Peter Zijlstra]

On Thu, Jun 11, 2015 at 09:34:30AM -0700, Andi Kleen wrote:
> 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.

The _existing_ ones expose timing of _other_ tasks, the proposed one does
not.
--
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/