Re: [Qemu-devel] Performance issues with -usb

[Brad Campbell]

Lonnie Mendez wrote:

>    Perhaps tweaking the value of ep_bInterval for the tablet's status
> change endpoint would help?  The endpoint descriptor for the tablet
> currently has this at 3 milliseconds.  The hid mouse reports a 10
> millisecond polling interval.

Indeed. I'm not quite sure how or why I did that in the 1st place as the tablet started life as a 
copy of the mouse in any case.

I've had good drag through the specs and all the data sheets for mouse chips I could find out there 
and most of them seem to recommend a value no faster than 8ms.

This drops the cpu utilisation of a Windows guest while idle about 75% when 
using -usbdevice tablet
I've not noticed any change in usability or mouse responsiveness.
(I played with values up to 0xFF but after about 0x20 there seemed to be 
immeasurable/no difference)


Index: hw/usb-hid.c
===================================================================
RCS file: /cvsroot/qemu/qemu/hw/usb-hid.c,v
retrieving revision 1.5
diff -u -r1.5 usb-hid.c
--- hw/usb-hid.c        19 Jul 2006 18:06:15 -0000      1.5
+++ hw/usb-hid.c        24 Jul 2006 09:55:22 -0000
@@ -169,7 +169,7 @@
        0x81,       /*  u8  ep_bEndpointAddress; IN Endpoint 1 */
        0x03,       /*  u8  ep_bmAttributes; Interrupt */
        0x08, 0x00, /*  u16 ep_wMaxPacketSize; */
-       0x03,       /*  u8  ep_bInterval; (255ms -- usb 2.0 spec) */
+       0x20,       /*  u8  ep_bInterval; (255ms -- usb 2.0 spec) */


Brad
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