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Date: Thu, 20 Dec 2012 07:54:46 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] Performance of usb tablet over ehci
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To: Hao Luo <luo_brian@126.com>
Cc: Hans de Goede <hdegoede@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

On 12/19/12 18:48, Hao Luo wrote:
> Gerd,
> 
> Thanks very much.
> 
> I tried to install usb 3.0 driver in win7 guest, and the cpu load
> decreased to about 9%, as much as PS2 mouse emulation.

Good to see this actually meets the expectations ;)

> BTW, there are >90 fds polled by qemu_iohandler_poll(). According to
> the perf profiling report, when uhci hid mouse is enabled, this
> function will be called much more frequently than using PS2 mouse.

Yes.  It's called each time qemu goes sleep, even if sleeping for a very
short time only.

> Any source code or functions I should refer to so that I can find out
> which fds take most of CPU time?

The problem isn't the high number of fds, the problem which causes the
high load is the high wakeup rate needed by uhci emulation (which is
largely dictated by the design of the hardware we are emulating).

cheers,
  Gerd