Re: [RFC PATCH 0/3]perf/core: extend perf_reg and perf_sample_regs_intr

[Peter Zijlstra]

On Fri, Nov 06, 2015 at 09:04:00PM +1100, Michael Ellerman wrote:
> It's a perrenial request from our hardware PMU folks to be able to see the raw
> values of the PMU registers.
> 
> I think partly it's so that they can verify that perf is doing what they want,
> and some of it is that they're interested in some of the more obscure info that
> isn't plumbed out through other perf interfaces.
> 
> We've used various internal hacks over the years to keep them happy. This is an
> attempt to use a somewhat standard mechanism.
> 
> It would also be helpful for those of us working on the perf hardware backends,
> to be able to verify that we're programming things correctly, without resorting
> to debug printks etc.
> 
> Basically we want to sample regs at the time of the perf interrupt, so we
> though PERF_SAMPLE_REGS_INTR made senes :)
> 
> But if you think this is the wrong mechanism within perf, then please let us
> know.
> 
> I know perf's mission is to abstract as much of the arcane hardware details
> into a generic interface and make PMUs actually useful for normal folks, and we
> are committed to that, but it would also be useful to be able to get the raw
> values for a different type of user.
> 
> Maddy's patch only exports PMC1-6 and MMCR0/1. I think we also need to export
> some others, in particular MMCRA has a lot of stuff in it, half of which is not
> even architected. So that would have to be exported as "POWER8_MMCRA". And then
> there's the SIAR/SDAR/SIER which contain a bunch of info on sampled
> instructions that is not currently plumbed out.

OK, no objections then. But this is useful information and should be
included in the patch set.
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