linux-kernel - Re: perf events over (net) console?

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Date:	Thu, 09 Sep 2010 14:47:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Harald Gustafsson <hgu1972@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Harald Gustafsson <harald.gustafsson@...csson.com>,
	Song Yuan <song.yuan@...csson.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: perf events over (net) console?

On Thu, 2010-09-09 at 14:31 +0200, Harald Gustafsson wrote:

> Sorry for being daft...

No worries, I'm sure we all qualify at times ;-)

> >> >
> >> > You need a process context anyway to read the data and send it to
> >> > whatever place you want it.
> >> >
> >> > Putting that in-kernel serves no purpose what so ever.
> >>
> >> But if we bring the splice support, that can be done with minimal
> >> userspace noise. Plus that would work with the usual sockets but not
> >> limited to that.
> >
> > Yes. If we can transform the data over the network without it touching
> > disk, then that would be a sufficiently 'does not disturb other tasks'
> > measurement method.
> 
> Thanks for the pointers to more information, and yes my thoughts was
> more about avoiding the data copy then avoiding any processing context
> at all.

Right, currently you get a single copy with mmap() + write(), once we
manage to fix splice() and actually provide perf-splice() you'd be able
to do zero-copy.


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