linux-kernel - Re: Perf and ftrace [was Re: PyTimechart]

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Message-ID: <20100512170734.GA15953@Krystal>
Date:	Wed, 12 May 2010 13:07:34 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Pierre Tardy <tardyp@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	linux-kernel@...r.kernel.org, arjan@...radead.org,
	ziga.mahkovec@...il.com, davem <davem@...emloft.net>
Subject: Re: Perf and ftrace [was Re: PyTimechart]

* Peter Zijlstra (peterz@...radead.org) wrote:
> On Wed, 2010-05-12 at 18:46 +0200, Frederic Weisbecker wrote:
> > But there is no strong reason for perf record not to use splice,
> > a part the fact that perf doesn't support splice.
> > 
> Its mostly an interface/api question. You cannot easily splice() a
> mmap()'ed buffer on machines that have address constraints like sparc.

Ah ? Can you explain this issue a bit more ? There is possibly a concern I don't
quite see here.

Thanks,

Mathieu

> 
> The thing I was thinking about is adding a new syscall that creates a
> single buffer of specified size and provides a fd. Then use
> PERF_EVENT_IOC_SET_OUTPUT, to connect an event to that fd/buffer and use
> splice() on that fd.
> 
> It could reuse most of the perf buffer code, but simply not map it into
> userspace and therefore not have the restriction on the vaddr.
> 
> Once you have that, a .splice_read implementation shouldn't be too hard.
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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