Re: perf_counters: page fault trace record

[Corey Ashford]

Ingo Molnar wrote:
> * Paul Mackerras <paulus@xxxxxxxxx> 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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