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Subject: Re: perf events over (net) console?
From: Peter Zijlstra <peterz@infradead.org>
To: Harald Gustafsson <hgu1972@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, Frederic Weisbecker <fweisbec@gmail.com>,
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        Steven Rostedt <rostedt@goodmis.org>
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Date: Thu, 09 Sep 2010 14:47:33 +0200
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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.