Re: [PATCH] perf_events: fix bug in hw_perf_enable()

[Stephane Eranian]

On Mon, Feb 1, 2010 at 5:04 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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
>>
>> Âstatic struct event_constraint intel_core2_event_constraints[] =
>> Â{
>> - Â Â Â FIXED_EVENT_CONSTRAINT(0xc0, (0x3|(1ULL<<32))), /* INSTRUCTIONS_RETIRED */
>> - Â Â Â FIXED_EVENT_CONSTRAINT(0x3c, (0x3|(1ULL<<33))), /* UNHALTED_CORE_CYCLES */
>> + Â Â Â FIXED_EVENT_CONSTRAINT(0x00c0, 1ULL << 32), /* INST_RETIRED.ANY */
>> + Â Â Â FIXED_EVENT_CONSTRAINT(0x003c, 1ULL << 33), /* CPU_CLK_UNHALTED.CORE */
>> + Â Â Â /*
>> + Â Â Â Â* FIXED_EVENT_CONSTRAINT(0x013c, 1ULL << 34), ÂCPU_CLK_UNHALTED.REF
>> + Â Â Â Â*
>> + Â Â Â Â* Core2 has Fixed Counter 2 listed as CPU_CLK_UNHALTED.REF and event
>> + Â Â Â Â* 0x013c as CPU_CLK_UNHALTED.BUS and specifies there is a fixed
>> + Â Â Â Â* ratio between these counters.
>> + Â Â Â Â*
>> + Â Â Â Â* TODO: find/measure the fixed ratio and apply it so that we can
>> + Â Â Â Â* enable this fixed purpose counter in a transparent way.
>> + Â Â Â Â*/
>> Â Â Â Â INTEL_EVENT_CONSTRAINT(0x10, 0x1), /* FP_COMP_OPS_EXE */
>> Â Â Â Â INTEL_EVENT_CONSTRAINT(0x11, 0x2), /* FP_ASSIST */
>> Â Â Â Â 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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Stephane Eranian  | EMEA Software Engineering
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