linux-kernel - Re: comments on Performance Counters for Linux (PCL)

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Message-Id: <1243629142.6645.108.camel@laptop>
Date:	Fri, 29 May 2009 22:32:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	eranian@...il.com
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Robert Richter <robert.richter@....com>,
	Paul Mackerras <paulus@...ba.org>,
	Andi Kleen <andi@...stfloor.org>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <cel@...ibm.com>,
	Corey J Ashford <cjashfor@...ibm.com>,
	Philip Mucci <mucci@...s.utk.edu>,
	Dan Terpstra <terpstra@...s.utk.edu>,
	perfmon2-devel <perfmon2-devel@...ts.sourceforge.net>
Subject: Re: comments on Performance Counters for Linux (PCL)

On Thu, 2009-05-28 at 18:25 +0200, Peter Zijlstra wrote:
> >   10/ Group event buffer entry
> > 
> >        This is activated by setting the PERF_RECORD_GROUP in the record_type
> >        field.  With this bit set, the values of the other members of the
> >        group are stored sequentially in the buffer. To help figure out which
> >        value corresponds to which event, the current implementation also
> >        stores the raw encoding of the event.
> > 
> >        The event encoding does not help figure out which event the value refers
> >        to. There can be multiple events with the same code. This does fit the
> >        API model where events are identified by file descriptors.
> > 
> >        The file descriptor must be provided and not the raw encoding.
> 
> OK, sounds sensible.

This can't actually be done, fds can change, and there is no struct
file* to fd map.

If the config isn't good enough, the best we could do is something
unique per instance.

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