linux-kernel - Re: [PATCH] perf report: Display per-thread event counters

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Date:	Sat, 8 Aug 2009 18:13:42 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Brice Goglin <Brice.Goglin@...ia.fr>
Cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, paulus@...ba.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf report: Display per-thread event counters


* Brice Goglin <Brice.Goglin@...ia.fr> wrote:

> Ingo Molnar wrote:
> >> [...] But I don't see yet where I am suppose to get something like 
> >> PERF_READ_EVENT in builtin-stat.c so I haven't touched it yet.
> >>     
> >
> > Yeah. 'perf stat' is not really getting events but is doing a 
> > read-out of the counter value(s) and constructs its 'read event' 
> > that way. So you wont find PERF_READ_EVENT in builtin-stat.c, you'll 
> > find:
> >
> >                 res = read(fd[cpu][counter], single_count, nv * sizeof(u64));
> >
> > in read_counter(). The printout is then done in print_counter().
> 
> Is there a way to get per-thread counters there? I wrote the code 
> to gather per-cpu counters there, but I don't see any way to get 
> the corresponding thread-id.
> 
> I looked at perf record to get some help. But I don't see where 
> the PERF_EVENT_READ are generated. I guess they are directly 
> generated by the kernel, read by perf record, and written as is to 
> the output file?

Inherited counters are not accessible to the parent context. (they 
dont even have any fds instantiated, for performance and 
transparency reasons.)

I think perf stat could be enhanced to work not via reading the raw 
counters but by doing a mini "perf-record" internally, mmap the 
samples buffer and getting all the events there?

	Ingo
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