linux-kernel - Re: [PATCH] perf: do not flush maps on COMM for perf report

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Message-ID: <50353169.1080606@gmail.com>
Date:	Wed, 22 Aug 2012 13:22:17 -0600
From:	David Ahern <dsahern@...il.com>
To:	Luigi Semenzato <semenzato@...omium.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	Alexander Viro <viro@...iv.linux.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Robert Richter <robert.richter@....com>,
	linux-kernel@...r.kernel.org, sonnyrao@...omium.org,
	olofj@...omium.org, eranian@...gle.com
Subject: Re: [PATCH] perf: do not flush maps on COMM for perf report

On 8/21/12 3:52 PM, Luigi Semenzato wrote:
> This fixes a long-standing bug caused by the lack of separate
> COMM and EXEC record types, which makes "perf report" lose
> track of symbols when a process renames itself.
>
> With this fix (suggested by Stephane Eranian), a COMM (rename)
> no longer flushes the maps, which is the correct behavior.
> An EXEC also no longer flushes the maps, but this doesn't
> matter because as new mappings are created (for the executable
> and the libraries) the old mappings are automatically removed.
> This is not by accident: the functionality is necessary because
> DLLs can be explicitly loaded at any time with dlopen(),
> possibly on top of existing text, so "perf report" handles
> correctly the clobbering of new mappings on top of old ones.
>
> An alternative patch (which I proposed earlier) would be to
> introduce a separate PERF_RECORD_EXEC type, but it is a much
> larger change (about 300 lines) and is not necessary.
>
> Signed-off-by: Luigi Semenzato <semenzato@...omium.org>
> ---
>   tools/perf/util/thread.c |    1 -
>   1 files changed, 0 insertions(+), 1 deletions(-)
>
> diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> index fb4b7ea..8b3e593 100644
> --- a/tools/perf/util/thread.c
> +++ b/tools/perf/util/thread.c
> @@ -39,7 +39,6 @@ int thread__set_comm(struct thread *self, const char *comm)
>   	err = self->comm == NULL ? -ENOMEM : 0;
>   	if (!err) {
>   		self->comm_set = true;
> -		map_groups__flush(&self->mg);
>   	}
>   	return err;
>   }
>

Acked-by: David Ahern <dsahern@...il.com>
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