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Subject: Re: [RFC][PATCH v2 11/11] perf top: demo of how to use the sysfs
 interface
From: Lin Ming <ming.m.lin@intel.com>
To: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
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Date: Thu, 20 May 2010 09:17:29 +0800
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On Thu, 2010-05-20 at 02:18 +0800, Corey Ashford wrote:
> 
> On 5/18/2010 6:49 PM, Lin Ming wrote:
> > Just a temporary patch to show how to use the pmu sysfs interface...
> > 
> > Signed-off-by: Lin Ming <ming.m.lin@intel.com>
> > ---
> >  tools/perf/builtin-top.c |   13 +++++++++++++
> >  1 files changed, 13 insertions(+), 0 deletions(-)
> > 
> > diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> > index adc179d..eaa9405 100644
> > --- a/tools/perf/builtin-top.c
> > +++ b/tools/perf/builtin-top.c
> > @@ -1206,6 +1206,7 @@ static void start_counter(int i, int counter)
> >  	struct perf_event_attr *attr;
> >  	int cpu;
> >  	int thread_index;
> > +	int sys_fd;
> > 
> >  	cpu = profile_cpu;
> >  	if (target_tid == -1 && profile_cpu == -1)
> > @@ -1226,9 +1227,21 @@ static void start_counter(int i, int counter)
> > 
> >  	for (thread_index = 0; thread_index < thread_num; thread_index++) {
> >  try_again:
> > +		/*
> > +		 * This is just an ugly demo of how to use the sysfs interface.
> > +		 * You can also parse the <event-name> and open sys file as,
> > +		 * sys_fd = open("/sys/devices/system/cpu/events/<event-name>/event_source/id", O_RDONLY);
> > +		 */
> 
> In this above case, does this sys_fd also specify the event I am going to open, in addition to its event source?  I'd assume not since event_source is a symlink to /sys/devices/system/cpu/event_source (right?)

Right, this sys_fd only specifies the event source.

> How do I specify the exact event id via the sysfs interface?

/sys/devices/system/cpu/events/<event-name>/id

But in this patch series, the event id sysfs interface is not used yet.

Thanks,
Lin Ming

> 
> Thanks,
> 
> - Corey
>