Subject: Re: [RFC PATCH 0/3]perf/core: extend perf_reg and
 perf_sample_regs_intr
To: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>
References: <1446669978-6366-1-git-send-email-maddy@linux.vnet.ibm.com>
 <20151105130716.GC3604@twins.programming.kicks-ass.net>
 <20151106025844.GA28859@us.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Stephane Eranian <eranian@gmail.com>,
        Russell King <linux@arm.linux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Michael Ellerman <mpe@ellerman.id.au>
From: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Message-ID: <563C5AFD.9040102@linux.vnet.ibm.com>
Date: Fri, 6 Nov 2015 13:17:09 +0530
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On Friday 06 November 2015 08:28 AM, Sukadev Bhattiprolu wrote:
> Peter Zijlstra [peterz@infradead.org] 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

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