linux-kernel - Re: [PATCH 3/3] perf record: mmap output file

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Date:	Tue, 15 Oct 2013 18:37:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	David Ahern <dsahern@...il.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 3/3] perf record: mmap output file

On Tue, Oct 15, 2013 at 06:06:46PM +0200, Ingo Molnar wrote:
> 
> splice() is very fast and should be able to process a lot of pages in one 
> go, so the feedback loop should be pretty weak. mmap() triggers kernel 
> code as well, every time we run out of the 64 MB window we got to remap 
> it, right?
> 
> But that's all just theory - I think non-temporal stores have a pretty 
> good chance of being a very good solution as well.

The first write to a fresh page will also cause kernel code to be ran. We fault
and run mk_write, which will end up doing block allocation etc..
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