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

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Date:	Tue, 15 Oct 2013 11:32:45 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	David Ahern <dsahern@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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

Em Tue, Oct 15, 2013 at 08:04:15AM -0600, David Ahern escreveu:
> On 10/8/13 11:59 PM, Ingo Molnar wrote:
> > 2)

> > Yet another method would be to avoid the copies altogether via the splice
> > system-call - see:

> >	git grep splice kernel/trace/

> > To make splice low-overhead we'd have to introduce a mode to not mmap
> > the data part of the perf ring-buffer and splice the data straight
> > from the perf fd into a temporary pipe and over from the pipe into
> > the target file (or socket).

> I looked into splice and it was not clear it would be a good match.
> First, perf is setup to pull data from mmap's and there is not a 1:1
> association between mmap's and fd's (fd_in for splice). Second and

Jiri and PeterZ probaby will have comments here... ;-) :-)

Jiri even have patches, IIRC.

- Arnaldo
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