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

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Date:	Thu, 9 Sep 2010 13:40:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
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>
Subject: Re: perf events over (net) console?


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Thu, Sep 09, 2010 at 01:19:01PM +0200, Peter Zijlstra wrote:
> > On Thu, 2010-09-09 at 13:06 +0200, Harald Gustafsson wrote:
> > > Hi,
> > > 
> > > We would like to monitor the perf events continuously on a remote 
> > > machine. Does it exist a solution (in the kernel) to direct the 
> > > output to a console or maybe even a netconsole? We would like to 
> > > avoid a user space application to transfer it, due to that the 
> > > machine will be running a test which will heavily load it and we 
> > > want to avoid as many unrelated user space tasks as possible. If 
> > > not mainlined does anyone have a patch for this?
> > 
> > No, and its a daft requirement.
> > 
> > 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,

	Ingo
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