Re: [PATCH 00/13] Add support for perf_arch_regs

[Madhavan Srinivasan]

On Tuesday 30 August 2016 09:31 PM, Nilay Vaish wrote:
> On 28 August 2016 at 16:00, Madhavan Srinivasan
> <maddy@xxxxxxxxxxxxxxxxxx> wrote:
> > Patchset to extend PERF_SAMPLE_REGS_INTR to include
> > platform specific PMU registers.
> >
> > Patchset applies cleanly on tip:perf/core branch
> >
> > It's a perennial request from hardware folks to be able to
> > see the raw values of the pmu registers. Partly it's so that
> > they can verify 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.
> >
> > Over the years internally we have used various hack to get
> > the requested data out but this is an attempt to use a
> > somewhat standard mechanism (using PERF_SAMPLE_REGS_INTR).
> >
> > This 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.
> >
> > Mechanism proposed:
> >
> > 1)perf_regs structure is extended with a perf_arch_regs structure
> > which each arch/ can populate with their specific platform
> > registers to sample on each perf interrupt and an arch_regs_mask
> > variable, which is for perf tool to know about the perf_arch_regs
> > that are supported.
> >
> > 2)perf/core func perf_sample_regs_intr() extended to update
> > the perf_arch_regs structure and the perf_arch_reg_mask. Set of new
> > support functions added perf_get_arch_regs_mask() and
> > perf_get_arch_reg() to aid the updates from arch/ side.
> >
> > 3) perf/core funcs perf_prepare_sample() and perf_output_sample()
> > are extended to support the update for the perf_arch_regs_mask and
> > perf_arch_regs in the sample
> >
> > 4)perf/core func perf_output_sample_regs() extended to dump
> > the arch_regs to the output sample.
> >
> > 5)Finally, perf tool side is updated to include a new element
> > "arch_regs_mask" in the "struct regs_dump", event sample funcs
> > and print functions are updated to support perf_arch_regs.
> I read the patch series and I have one suggestion to make.  I think we
> should not use 'arch regs' to refer to these pmu registers.  I think
Reason is that they are arch specific pmu regs. But I guess we can go with
pmu_regs also. And having a "pregs" as option to list in -I? will be fine?
(patch 13 in the patch series)


Maddy

> architectural registers typically refer to the ones that hold the
> state of the process.  Can we replace arch_regs by pmu_regs, or some
> other choice?
>
> Thanks
> Nilay