linux-kernel - Re: [PATCH] x86, perf: Use INST_RETIRED.PREC

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Date:	Wed, 21 Oct 2015 18:55:42 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <ak@...ux.intel.com>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86, perf: Use INST_RETIRED.PREC_DIST for cycles:pp on
 Skylake

On Wed, Oct 21, 2015 at 06:52:52PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 21, 2015 at 08:26:08AM -0700, Andi Kleen wrote:
> > So it turns out that UOPS_RETIRED.ALL+pebs only works by accident
> > on Skylake. It's not in the specification.
> 
> Accident or not, it works and you've tested it. Might as well keep it.
> Specs can be updated.

No, it's better not to use it.

> Also, even with the SNB 'hickup' they still haven't got the memo that
> cycles is important for PEBS ?

INST_RETIRED.PREC_DIST is a far better cycles than UOPS_RETIRED.ALL
(see my earlier example)

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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