linux-kernel - Re: [PATCH v2] perf tools: Start the perf.data mapping at data offset in perf trace

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Date:	Wed, 7 Oct 2009 00:29:26 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Tom Zanussi <tzanussi@...il.com>
Subject: Re: [PATCH v2] perf tools: Start the perf.data mapping at data
	offset in perf trace

On Tue, Oct 06, 2009 at 09:21:26PM +0200, Frederic Weisbecker wrote:
> Currently, we are mapping perf.data in the beginning of the file
> and use the data offset as a buffer offset. This may exceed the
> mapping area if the data offset is upper than page_size * mmap_window
> and result in a page fault (thing that happen if we merge trace.info
> in perf.data).
> 
> Instead, let's start the mapping in the page that matches our data
> offset.
> 
> v2: Drop a junk from another patch (trace_report() removal)
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Mike Galbraith <efault@....de>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Tom Zanussi <tzanussi@...il.com>


I just tested the trace.info drop with perf sched, and we have the same bug
with mmap.

I guess we should rather have a common helper to use mmap on perf.data
and rely on a callback to process the events.
I'm putting this in my TODO list.

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