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Date: Tue, 24 Jul 2012 11:02:04 +0100
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From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] [RFC PATCH 0/6] virtio-trace: Support virtio-trace
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To: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>, Arnd Bergmann <arnd@arndb.de>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Frederic Weisbecker <fweisbec@gmail.com>, Dhaval Giani <dhaval.giani@gmail.com>, qemu-devel@nongnu.org, Borislav Petkov <bp@amd64.org>, linux-kernel@vger.kernel.org, "Franch Ch. Eigler" <fche@redhat.com>, Ingo Molnar <mingo@redhat.com>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Steven Rostedt <rostedt@goodmis.org>, Anthony Liguori <anthony@codemonkey.ws>, yrl.pp-manager.tt@hitachi.com, Amit Shah <amit.shah@redhat.com>, virtualization@lists.linux-foundation.org, Srikar Dronamraju <srikar@linux.vnet.ibm.com>

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