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Date: Wed, 7 Oct 2009 00:29:26 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: LKML <linux-kernel@vger.kernel.org>, Peter Zijlstra <peterz@infradead.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Mike Galbraith <efault@gmx.de>, Paul Mackerras <paulus@samba.org>,
       Tom Zanussi <tzanussi@gmail.com>
Subject: Re: [PATCH v2] perf tools: Start the perf.data mapping at data
	offset in perf trace
Message-ID: <20091006222924.GA11007@nowhere>
References: <1254856626-10286-1-git-send-email-fweisbec@gmail.com> <1254856886-10348-1-git-send-email-fweisbec@gmail.com>
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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@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Mike Galbraith <efault@gmx.de>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Tom Zanussi <tzanussi@gmail.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.