Re: perf events over (net) console?
From: Ingo Molnar
Date: Thu Sep 09 2010 - 09:07:40 EST
* Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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@hostname record sleep 60
perf --remote user@hostname 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/