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SubjectRe: perf_counters: page fault trace record
Ingo Molnar wrote:
> * Paul Mackerras <paulus@samba.org> wrote:
>
>> Corey Ashford writes:
>>
>>> Paul Mackerras wrote:
>>>> Can't you do what you need just using a page fault software
>>>> counter with sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR
>>>> and sample_period = 1?
>>> I thought about that, but I was under the (incorrect?)
>>> impression that on Power, the PERF_SAMPLE_ADDR would be set by
>>> the value of the SDAR register, which wouldn't be correct for
>>> the case of a page fault.
>> No, the PERF_SAMPLE_ADDR value only comes from SDAR for a hardware
>> counter overflow event. For the page-fault software counter the
>> PERF_SAMPLE_ADDR value will always be the faulting address.
>
> Corey, could you please add support for it in 'perf'? We dont want
> such sw-counter features to be in the kernel code without matching
> support in tools/perf/.
>
> While user data symbols wont be resolved, if we have a
> --target-address switch in perf record we could see the faulting
> frequency (and the fault coverage - and ordering as well) of shared
> libraries, in perf report and perf annotate.
>
> This would be a very useful facility.
>
> Thanks,
>
> Ingo

I'll see what I can do. This will be my first time modifying perf, so expect
that I won't do things the way you prefer the first couple of go-arounds :)

Regards,

- Corey




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