linux-kernel - [RFC] [PATCH 1/1] perf: add support for arch-dependent symbolic event names to "perf stat"

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Message-ID: <4B8F1B58.5000702@linux.vnet.ibm.com>
Date:	Wed, 03 Mar 2010 18:30:48 -0800
From:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [RFC] [PATCH 1/1] perf: add support for arch-dependent symbolic event
 names to "perf stat"

For your review, this patch adds support for arch-dependent symbolic event names 
to the "perf stat" tool, and could be expanded to other "perf *" commands fairly 
easily, I suspect.

To support arch-dependent event names without adding arch-dependent code to 
perf, I added a callout mechanism whereby perf will look for the environment 
variable: PERF_ARCH_DEP_LIB, and if it exists, it will try to open it as a 
shared object.  If that succeeds, it looks for the symbol 
"parse_arch_dep_event".  If that exists, that function will be called by 
parse_events() before all of the other event parsing functions in 
parse-events.c.  It is passed the same arguments as the other parse_*_event 
functions, namely the event string and a pointer to an event attribute structure.

As the code existed, "perf stat" would print out the count results, but for raw 
events (which is how arch-dependent events are supported in perf_events), it 
would just print out a raw code.  This is not acceptable, especially when a 
symbolic name was placed on the command line.  So I changed the code to save 
away the event name that was passed on the command line, rather than doing a 
reverse translation to an event string based on the event type and config fields 
of the attr structure.  In this way, there's no need for a reverse translation 
function in the arch-dependent library; only a event string->attr struct 
function is needed.

I could well be missing something, but I don't understand why reverse 
translation is ever needed in perf, as long as the tool keeps track of the 
original event strings.

Thanks for your consideration,

- Corey

Corey Ashford
Software Engineer
IBM Linux Technology Center, Linux Toolchain
Beaverton, OR
503-578-3507
cjashfor@...ibm.com

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