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    SubjectRe: [RFC PATCH 0/6] virtio-trace: Support virtio-trace
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    On Tue, Jul 24, 2012 at 3:36 AM, Yoshihiro YUNOMAE
    <yoshihiro.yunomae.ez@hitachi.com> 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.

    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.

    Are you using text formatted ftrace?

    Stefan


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