Re: [Qemu-devel] Re: ehci update

["David S. Ahern" <daahern@cisco.com>]

On 04/13/2010 07:20 PM, Alexander Graf wrote:
>>>> It still needs a lot of love, but definitely an improvement from the
>>>> last version. The biggest difference for the performance boost and
>>>> stability is discovering that the usbfs in linux limits transactions to
>>>> 16k versus the EHCI spec which allows 20k per qTD. I added a hack to
>>>> submit which detects 20k requests from a guest and breaks it up into 2
>>>> requests through the host (a 16k and then a 4k).
>>>
>>> Did someone already bring this up on LKML or wherever usbfs is
>>> discussed? Should be fixable, I naively guess.
>>
>> I submitted the patch to linux-usb and it was nack'ed. The response was
>> that memory is allocated in powers of 2 so trying to up the limit from
>> 16k to 20k means it will actually want to find 32k of contiguous memory.
>> The suggestion was to handle it with multiple requests within qemu. I
>> guess libusb does that.
> 
> Any reason we're not using libusb?

Good question. I was wondering the same. I was going to look at
converting usb-linux to use libusb1 when I get some time.

David

> 
> 
> Alex
>