linux-kernel - Re: [V3][PATCH 0/7] perf, x86: Implement AMD IBS

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Date:	Tue, 4 Oct 2011 10:54:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Robert Richter <robert.richter@....com>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Don Zickus <dzickus@...hat.com>,
	acme <acme@...stprotocols.net>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [V3][PATCH 0/7] perf, x86: Implement AMD IBS


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

> On Fri, 2011-09-23 at 14:20 +0200, Robert Richter wrote:
> > > The only thing I'm not quite sure on is the userspace bits, but those
> > > are in the future work section as well, but possibly Ingo has a strong
> > > opinion here, sadly he doesn't have email atm :/
> > 
> > With Lin's patch 'perf: Remove perf_event_attr::type check' we already
> > can sample with perf record.
> > 
> > I think we could extend perf report to parse also ibs samples. 
> > The only thing we need for it should be the pmu name/type mapping 
> > in the perf.data header and the pmu type in the sample. See my 
> > comment on Stephane's patch '[PATCH] perf: make perf.data more 
> > self-descriptive (v5)'.
> 
> OK, so Ingo really really wants to see a little more perf 
> integration there. Acme, what's the state of Stephane's patch?

So the whole IBS thing looks quite unintegrated to me - and that's 
partly because the hw is admittedly weird. The way we could perhaps 
live with it upstream is two conditions:

 - Testable IBS user-space code a bit more prominently integrated
   than having to go down into a cellar with no working lights and 
   finding the code on display in tools/perf/Documentation/examples/ 
   on the bottom of a locked filing cabinet stuck in a disused
   lavatory with a sign on the door saying 'Beware of the Leopard.'

 - Only root/privileged users should be able to access it. Right now
   i think it's root-only due to percpu restrictions, but wanted to 
   mention it that this is an explicit requirement.

Non-privileged IBS use could be enabled by having working integration 
with generic events: we could add a upos generic event for example so 
IBS could map to '-e uops:p' or such, to allow skid-less profiling on 
AMD CPUs.

Thanks,

	Ingo
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