linux-kernel - Re: [rfc] Describe events in a structured way via sysfs

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Date:	Tue, 20 Jul 2010 17:19:20 +0200
From:	Robert Richter <robert.richter@....com>
To:	Lin Ming <ming.m.lin@...el.com>
CC:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Johannes Berg <johannes@...solutions.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Greg KH <greg@...ah.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	"eranian@...il.com" <eranian@...il.com>,
	"Gary.Mohr@...l.com" <Gary.Mohr@...l.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Will Deacon <will.deacon@....com>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <carll@...ibm.com>,
	Kay Sievers <kay.sievers@...y.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [rfc] Describe events in a structured way via sysfs

On 20.07.10 01:48:28, Lin Ming wrote:
 The caller reads config and type and pass them into perf_event_attr.
> 
> 1. Hardware events
> /sys/devices/system/cpu/cpu0...cpuN/events
> |-- L1-dcache-load-misses  ===> event name
> |   |-- config             ===> config value for the event
> |   `-- type               ===> event type

Wouldn't it be much easier to have a unique sysfs id (could be an
u64):

> |-- L1-dcache-load-misses  ===> event name
> |   `-- id                 ===> event id

... and then extend the syscall to enable an event by its sysfs id:

            memset(&attr, 0, sizeof(attr));
            attr.type        = PERF_TYPE_SYSFS;
            attr.sysfs_id    = sysfs_id;
            attr.sample_type = PERF_SAMPLE_CPU | PERF_SAMPLE_RAW;
            attr.config      = config;
	    ...

The kerrnel then knows which event is meant and the don't have to
provide event specific paramaters such as type/config that requires an
event specific setup. The advantage would be that we can open an event
file descriptor of every kind of event in a standardized way.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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