linux-kernel - Re: [RFC PATCH] perf: honoring cpuid for number of fixed counters

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Date:	Thu, 04 Jun 2015 14:30:37 +0200
From:	Imre Palik <imrep.amz@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, "Palik, Imre" <imrep@...zon.de>,
	Anthony Liguori <aliguori@...zon.com>
Subject: Re: [RFC PATCH] perf: honoring cpuid for number of fixed counters

On 06/04/15 13:49, Peter Zijlstra wrote:
> On Thu, Jun 04, 2015 at 12:35:08PM +0200, Imre Palik wrote:
>> On 06/03/15 10:36, Peter Zijlstra wrote:
>>> Further, the Intel Arch PerfMon v2 spec actually specifies there to be 3
>>> fixed function counters.
>>>
>>> So anything that says it is v2+ and does not have the 3, is non
>>> compliant.
>>>
>>> I would suggest you go fix your hypervisor.
>>
>> If I set up the hypervisor to advertise Arch PerfMon v1 (0 fixed
>> counters), then  without my patch, perf still tries to use fixed
>> counters.  So something is clearly broken here.
> 
> So the code you deleted does if (version > 1), and last I checked that
> should return false if version == 1.
> 
> So please check what's happening there first.

Checked, before sent my last mail.

The trouble is that the number of fixed counters is not taken into account when scheduling the events,
and the cpu model based event constraints will favour fixed counters.  So perf tries to use them.
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