Messages in this thread | | | Date | Sat, 13 Jun 2009 12:09:16 +0200 | From | Ingo Molnar <> | Subject | Re: perf_counters: page fault trace record |
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* 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
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