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Re: [Qemu-devel] Re: ehci update
From: |
Jan Kiszka |
Subject: |
Re: [Qemu-devel] Re: ehci update |
Date: |
Wed, 14 Apr 2010 21:38:40 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
David S. Ahern wrote:
>
> 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.
Will that overcome the 16k limit or just push the split-up into libusb?
Jan
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