linux-kernel - [PATCH 1/1] perf: Add support for arch- and processor-dependent symbolic event names

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Message-ID: <4B955941.4010505@linux.vnet.ibm.com>
Date:	Mon, 08 Mar 2010 12:08:33 -0800
From:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
To:	LKML <linux-kernel@...r.kernel.org>
CC:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>
Subject: [PATCH 1/1] perf: Add support for arch- and processor-dependent symbolic
 event names

This patch adds support for arch- and processor-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 the string 
value of that variable 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.

This patch was stimulated by the availability of Stephane Eranian's libpfm4 
which supports translating arch- and processor-specific symbolic event names and 
attributes to a perf_event_attr struct.  With a very thin layer on top of 
libpfm4, perf can make use of it with this patch.

Signed-off-by: Corey Ashford <cjashfor@...ux.vnet.ibm.com>

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