Re: [Xen-devel] pvusb performance

[Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>]

James,

> Okay maybe I'm a bit confused then.
>
> When Windows gave me a URB with 65536 bytes of data, I set buffer_length
> to 65536 and filled up the SG registers accordingly, but usbback gave me
> an error. When I break it into 512 byte (packet size) chunks it works
> okay. I just assumed that you have to give usbback requests with less
> that 'max packet size' of data.
>
> Maybe the cause of my error was somewhere else? I'll try it again.
If you transfer 65536 bytes of data, you should change the
USBIF_MAX_SEGMENTS_PER_REQUESTS value to 16 or more.
It is defined in include/xen/interface/io/usbif.h
You need to recompile the drivers.

Request size and MAX_RING_SIZE are trade-off.
I defined this value empirically.
If the value is about up to 20, it doesn't affect the performance
of memory stick.

Regards,
Noboru



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