linux-kernel - Re: [PATCH v8 02/14] perf: Add AUX area to ring buffer for raw data streams

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Date:	Mon, 17 Nov 2014 13:24:00 -0800
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com, markus.t.metzger@...el.com,
	mathieu.poirier@...aro.org, acme@...radead.org,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <michaele@....ibm.com>
Subject: Re: [PATCH v8 02/14] perf: Add AUX area to ring buffer for raw data
 streams

Alexander Shishkin [alexander.shishkin@...ux.intel.com] wrote:
| From: Peter Zijlstra <peterz@...radead.org>
| 
| This patch introduces "AUX space" in the perf mmap buffer, intended for
| exporting high bandwidth data streams to userspace, such as instruction
| flow traces.
| 
| AUX space is a ring buffer, defined by aux_{offset,size} fields in the
| user_page structure, and read/write pointers aux_{head,tail}, which abide
| by the same rules as data_* counterparts of the main perf buffer.

The "format" of this raw stream of data can differ across processors
(and architecutres) correct ? i.e the perf tool processing of this
aux data will also differ across processors ?

Power8 processors support what we call 24x7 counters that collect info
on a large number of events. The current 24x7 support in
(arch/powerpc/perf/hv-24x7.c) currently uses reading one counter at a
time using the pmu->read() interface.

We are looking for ways to export much larger number of counters through
one pmu->read() or another call. I am trying to see if the hv-24x7 pmu
could use this aux interface and then have/implement a helper in perf
tool to extract the counter values.

Sukadev

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