linux-kernel - Re: [PATCH 2/5] perf, x86: Enable PDIR precise instruction profiling on IvyBridge

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Date:	Fri, 6 Jul 2012 03:04:29 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 2/5] perf, x86: Enable PDIR precise instruction profiling
 on IvyBridge

On Thu, Jul 5, 2012 at 7:26 PM, Andi Kleen <ak@...ux.intel.com> wrote:
> On Thu, Jul 05, 2012 at 05:45:16PM +0200, Stephane Eranian wrote:
>> On Tue, Jul 3, 2012 at 6:04 AM, Andi Kleen <andi@...stfloor.org> wrote:
>> >> Well, the only way I can think of would be to request that the
>> >> event be programmed with exclusive mode ALWAYS. That
>> >> should not be to hard to add.
>> >
>> > I suspect it would need some special callbacks from the events core,
>> > that's why I only tried on IvyBridge.
>> >x
>> You could simply add a check in the x86 init code like what is done
>> with the pebs events and precise mode.
>
> Ah requiring the user to set exclusive? Maybe. Right now perf does not even
> have an option to set it. Would seem user unfriendly to me though.

Yes, that's what I meant since the beginning. Require exclusive mode
on the event is all we need to enforce the restriction. The scheduling
would still only work on counter 1.

I know that perf record/stat do not support this but given the new event
parser it should not too hard to add an excl term to the syntax. I have
that in libpfm4 now as an option on events. That's clearly a perf_event
option like period or freq and not a HW option like inv, edge.
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