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

From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
	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>
Subject: Re: [RFC PATCH  0/3]perf/core: extend perf_reg and perf_sample_regs_intr
Date: Thu, 5 Nov 2015 18:58:45 -0800	[thread overview]
Message-ID: <20151106025844.GA28859@us.ibm.com> (raw)
In-Reply-To: <20151105130716.GC3604@twins.programming.kicks-ass.net>

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.

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

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'.

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

Sukadev