Date:	Thu, 9 Sep 2010 15:21:00 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Harald Gustafsson <hgu1972@...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>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: perf events over (net) console?

On Thu, Sep 09, 2010 at 03:07:23PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > 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.
> 
> I think it would also be very useful to have some sort of tooling help 
> for "low overhead/impact perf recording".
> 
> If there's a 'target box' and a different 'host box' (where most of 
> development is done, etc.), then there might not be any NFS connection 
> set up to make zero-copy file transfer easy. Doing it over ssh would add 
> overhead.
> 
> One possible workflow would be to run this on the target/remote box:
> 
>   perf remote
> 
> And as long as that command is running there, it could be used from the 
> development box (over a trusted local network), using something like:
> 
>   perf --remote <hostname> record sleep 60
>   perf --remote <hostname> stat -a sleep 1
> 
> these would all do the measurements on the remote box, and the resulting 
> perf.data would be created on the desktop box. Communication would be 
> done via some well-known port.
> 
> etc.
> 
> An alternative implementation would be to drive this on the assumption 
> that an ssh connection can be established with the target box - but 
> followup high-volume data transfer would be done over an ordinary TCP 
> connection.
> 
> I.e. the workflow would be even simpler, something like:
> 
>   perf --remote user@...tname record sleep 60
>   perf --remote user@...tname stat -a sleep 1
> 
> Internally it would work by executing those commands on the remote box 
> via ssh, and redirecting the output via a TCP connection. (some other 
> details might be needed as well for splice to be usable in such a setup)
> 
> Would anyone be interested in having (and implementing ;-) this?
> 
> 	Ingo



In the beginning this could wrap into perf record - | perf pipe | netcat
and so, until we get the splice support.

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