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

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Date:	Thu, 9 Sep 2010 14:31:14 +0200
From:	Harald Gustafsson <hgu1972@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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?

2010/9/9 Ingo Molnar <mingo@...e.hu>:
>
> * 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.

Sorry for being daft...

>> >
>> > 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.

Regards,
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