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

From: Madhavan Srinivasan <[email-masked]>
Date: Fri, 6 Nov 2015 13:17:09 +0530

On Friday 06 November 2015 08:28 AM, Sukadev Bhattiprolu wrote:
> Peter Zijlstra [[email-masked]] wrote:
> | On Thu, Nov 05, 2015 at 02:16:15AM +0530, Madhavan Srinivasan wrote:
> | > Second patch updates struct arch_misc_reg for arch/powerpc with pmu registers
> | > and adds offsetof macro for the same. It extends perf_reg_value()
> | > to use reg idx to decide on struct to return value from.
> | 
> | Why; what's in those regs?
>
> Those are PMU control registers/counters (in Patch 2) that are of
> interest only in the context of a PMU interrupt and not relevant
> to ptrace itself.

Yes. Thats right.

> Could we add those registers to 'struct pt_regs' anyway?

I would prefer not to. Since as you mentioned, these are
not relevant to ptrace. Currently patch 2, adds only few
pmu registers, but would like to include more.
 
> We do have 'struct perf_regs' but that seems to be arch nuetral.
> If architectures could override that, maybe we could add these
> new registers there without touching 'struct pt_regs'.

Exactly, idea here is to capture more data using perf_sample_reg_intr
without extending pt_regs structure.

Maddy

> Even so, lot of perf code depends on 'struct pt_regs'.
>
> Sukadev