linux-kernel - Re: [PATCH 3/3] perf, x86: Add INST

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Date:	Mon, 23 Mar 2015 14:32:02 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 3/3] perf, x86: Add INST_RETIRED.ALL workarounds


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

> On Mon, Mar 23, 2015 at 11:39:00AM +0100, Ingo Molnar wrote:
> > > http://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/5th-gen-core-family-spec-update.pdf
> > > 
> > > BDM11 and BDM55 (not 57) tell us that the PMU will generate crap output
> > > if you don't do this. Non-fatal but gibberish.
> > 
> > Should be part of the changelog?
> 
> Sure, lemme go make that happen.
> 
> > So I did not say rounding up, I meant this sentence:
> > 
> > > > > + *   [...] We combine the two to enforce
> > > > > + * a min-period of 128.
> > 
> > IMO ambiguously suggests that the result of the combination of the two 
> > is to enforce a min-period of 128. Would somethin like this:
> > 
> > 	          We combine the two to enforce
> >           a min-period of 128, rounded (down) to multiples of 64.
> >           The original period is still kept by the core code and is 
> >           approximated in the long run via these slightly fuzzed 
> >           hardware-periods.
> 
> Like so then?

Yeah, looks good to me!

Thanks,

	Ingo
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