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

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Message-ID: <CAJSP0QW_2JJ0nf=NW0y30VSid2HSxaqb=mRGV8CTtAKj0ujDWw@mail.gmail.com>
Date:	Tue, 24 Jul 2012 11:02:04 +0100
From:	Stefan Hajnoczi <stefanha@...il.com>
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Cc:	linux-kernel@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Arnd Bergmann <arnd@...db.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com, qemu-devel@...gnu.org,
	Borislav Petkov <bp@...64.org>,
	virtualization@...ts.linux-foundation.org,
	"Franch Ch. Eigler" <fche@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Amit Shah <amit.shah@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval.giani@...il.com>
Subject: Re: [RFC PATCH 0/6] virtio-trace: Support virtio-trace

On Tue, Jul 24, 2012 at 3:36 AM, Yoshihiro YUNOMAE
<yoshihiro.yunomae.ez@...achi.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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