linux-kernel - Re: [PATCH 2/5] perf tool: Initialize events IDs in a single function

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Message-ID: <20111120010358.GE13052@ghostprotocols.net>
Date:	Sat, 19 Nov 2011 23:03:58 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	a.p.zijlstra@...llo.nl, mingo@...e.hu, paulus@...ba.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] perf tool: Initialize events IDs in a single
	function

Em Sat, Nov 19, 2011 at 08:36:21PM -0500, Jiri Olsa escreveu:
> On Fri, Nov 18, 2011 at 12:22:55PM -0200, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Nov 18, 2011 at 02:46:42PM +0100, Jiri Olsa escreveu:
> > > Currently events' IDs initialization is scattered among the
> > > code. Adding function 'perf_evlist__init_ids' to allocate
> > > and retrive events' IDs in one place.

> > I'm ok with this one, will merge it in my perf/core branch together with
> > a fix for a bug I noticed in the original code and that remains with
> > your changes: consider what happens if we do a second perf_evlist__mmap,
> > we will call perf_evlist__id_add_fd again and thus bump evsel->ids++
> > over nr_threads * nr_cpus, overflowing it.

> is there a valid scenario for this function to be called more than once?
> I'd think that just ensuring this is called once is enough

I don't know, I just don't want to preclude that, crystal balls are not
that reliable :-)

- Arnaldo
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