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Re: [Qemu-devel] Re: ehci update
From: |
David S. Ahern |
Subject: |
Re: [Qemu-devel] Re: ehci update |
Date: |
Tue, 13 Apr 2010 21:35:50 -0600 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 |
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
>