On Tue, Jul 24, 2012 at 12:03 PM, Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx> 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. Okay, thanks for explaining some of the ideas you have. I won't ask more because it's out of scope for this patch series :). Stefan _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
