linux-kernel - Re: [PATCH] perf_events: fix bug in hw_perf

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Date:	Mon, 1 Feb 2010 17:14:02 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com, robert.richter@....com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] perf_events: fix bug in hw_perf_enable()

On Mon, Feb 1, 2010 at 5:04 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2010-02-01 at 16:35 +0100, Peter Zijlstra wrote:
>> +++ linux-2.6/arch/x86/kernel/cpu/perf_event.c
>> @@ -243,8 +243,18 @@ static struct event_constraint intel_cor
>>
>>  static struct event_constraint intel_core2_event_constraints[] =
>>  {
>> -       FIXED_EVENT_CONSTRAINT(0xc0, (0x3|(1ULL<<32))), /* INSTRUCTIONS_RETIRED */
>> -       FIXED_EVENT_CONSTRAINT(0x3c, (0x3|(1ULL<<33))), /* UNHALTED_CORE_CYCLES */
>> +       FIXED_EVENT_CONSTRAINT(0x00c0, 1ULL << 32), /* INST_RETIRED.ANY */
>> +       FIXED_EVENT_CONSTRAINT(0x003c, 1ULL << 33), /* CPU_CLK_UNHALTED.CORE */
>> +       /*
>> +        * FIXED_EVENT_CONSTRAINT(0x013c, 1ULL << 34),  CPU_CLK_UNHALTED.REF
>> +        *
>> +        * Core2 has Fixed Counter 2 listed as CPU_CLK_UNHALTED.REF and event
>> +        * 0x013c as CPU_CLK_UNHALTED.BUS and specifies there is a fixed
>> +        * ratio between these counters.
>> +        *
>> +        * TODO: find/measure the fixed ratio and apply it so that we can
>> +        * enable this fixed purpose counter in a transparent way.
>> +        */
>>         INTEL_EVENT_CONSTRAINT(0x10, 0x1), /* FP_COMP_OPS_EXE */
>>         INTEL_EVENT_CONSTRAINT(0x11, 0x2), /* FP_ASSIST */
>>         INTEL_EVENT_CONSTRAINT(0x12, 0x2), /* MUL */
>
> >From what I can measure on the available Core2 systems this ratio is
> exactly 1, which would be consistent with the Nehalem and Westmere
> tables calling this event .REF
>
> Stephane, have you ever observed this ratio to be anything other than 1?
>

Using perfmon on Core 2 on a 10s noploop:

pfmon -eunhalted_reference_cycles,unhalted_core_cycles,cpu_clk_unhalted:bus
 noploop 10
noploop for 10 seconds
23869090125 UNHALTED_REFERENCE_CYCLES
23849336873 UNHALTED_CORE_CYCLES
 2652122099 CPU_CLK_UNHALTED:BUS


> If not, I think we can simply stick this counter back in and not worry
> about it.
>
>



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