Re: [tip:perf/core] perf/x86: Use INST_RETIRED.PREC_DIST for cycles: ppp

From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: vincent.weaver@maine.edu, jolsa@redhat.com,
	torvalds@linux-foundation.org, eranian@google.com,
	tglx@linutronix.de, acme@redhat.com, ak@linux.intel.com,
	linux-kernel@vger.kernel.org, hpa@zytor.com,
	linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perf/core] perf/x86: Use INST_RETIRED.PREC_DIST for cycles: ppp
Date: Wed, 9 Dec 2015 09:29:23 +0100	[thread overview]
Message-ID: <20151209082923.GA15254@gmail.com> (raw)
In-Reply-To: <20151208132753.GD6373@twins.programming.kicks-ass.net>

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Dec 08, 2015 at 09:57:07AM +0100, Peter Zijlstra wrote:
> > On Tue, Dec 08, 2015 at 09:50:26AM +0100, Peter Zijlstra wrote:
> > > On Tue, Dec 08, 2015 at 06:36:04AM +0100, Ingo Molnar wrote:
> > > 
> > > > So I checked my NHM box with your latest queue and it now works correctly. Do you 
> > > > have any idea what the difference is/was?
> > > 
> > > Sadly, no clue :/
> > > 
> > > I went over those patches and cannot find anything that should affect
> > > NHM (or <=SNB in fact).
> > 
> > Oh wait, I spoke too soon, the two new patches affect everything with
> > PEBS. And esp. the latter one:
> > 
> >   lkml.kernel.org/r/1449177740-5422-2-git-send-email-andi@firstfloor.org
> > 
> 
> If that is the patch that makes your NHM go again, then running 2
> concurrent perf-top sessions should make it all go dark again.

Hm, so I tried again your latest perf/urgent (1221fc3b3e3a) merged into tip:master 
(c9586e904a68), and booted it on the NHM, but 'perf top' refuses to break.

One thing that was special about my first NHM test was that it conducted an about 
24 hours perf stress. OTOH 'cycles:p' did work, it was only 'cycles:pp' that was 
producing no events whatsoever - so it wasn't a total breakage, only :pp related.

Weird ...

Thanks,

	Ingo