Re: Re: [RFC PATCH 0/6] virtio-trace: Support virtio-trace

[Yoshihiro YUNOMAE]

Hi Stefan,

Thank you for commenting on our patch set.

(2012/07/24 20:03), Masami Hiramatsu wrote:
> (2012/07/24 19:02), Stefan Hajnoczi wrote:
> > On Tue, Jul 24, 2012 at 3:36 AM, Yoshihiro YUNOMAE
> > <yoshihiro.yunomae.ez@xxxxxxxxxxx> wrote:
> > > The performance of each method is compared as follows:
> > >   [1] Native
> > >       - only recording trace data to ring-buffer on a guest
> > >   [2] Virtio-trace
> > >       - running a trace agent on a guest
> > >       - a reader on a host opens FIFO using cat command
> > >   [3] IVRing
> > >       - A SystemTap script in a guest records trace data to IVRing.
> > >         -- probe points are same as ftrace.
> > >   [4] Virtio-serial(normal)
> > >       - A reader(using cat) on a guest output trace data to a host using
> > >         standard output via virtio-serial.
> >
> > The first time I read this I thought you are adding a new virtio-trace
> > device.  But it looks like this series really add splice support to
> > virtio-console and that yields a big performance improvement when
> > sending trace_pipe_raw.
>
> Yes, sorry for the confusion. Actually this is an enhancement of
> virtio-serial. I'm working with Yoshihiro on this feature.
>
> > Guest ftrace is useful and I like this.  Have you thought about
> > controlling ftrace from the host?  Perhaps a command could be added to
> > the QEMU guest agent which basically invokes trace-cmd/perf.
>
> As you can see, guest trace-agent can be controlled via a
> control channel. In our scenario, host tools can control that
> instead of guest one.
>
> We are considering that exporting the tracing part of guest's
> debugfs to host via another virtio-serial channel by using
> 9pfs, so that the host tools can refer that.
>
> (In this scenario, guest trace-agent will also provide 9pfs server.
> Since it means that the agent can handle writing a special file,
> trace-agent can be controlled via the special file on exported
> debugfs.)
>
> Of course, this also requires modifying trace-cmd/perf to accept
> some options like guest-debugfs mount point, guest's serial
> channel pipe (or unix socket?), etc. However, it will be a small
> change.
>
> Thank you,

>> Are you using text formatted ftrace?
No, currently using raw format, butãwe'd like to reformat it in text.

Thank you,

--
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@xxxxxxxxxxx


--
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/