[PATCH v2 4/4] USB: EHCI: support running URB giveback in tasklet context

[Ming Lei]

On Mon, Jun 24, 2013 at 6:24 PM, Oliver Neukum <oliver at neukum.org> wrote:
> On Monday 24 June 2013 17:42:05 Ming Lei wrote:
>> All 4 transfer types can work well on EHCI HCD after switching to run
>> URB giveback in tasklet context, so mark all HCD drivers to support
>> it.
>>
>> At the same time, don't release ehci->lock during URB giveback,
>> and remove the check on HCD_BH in ehci_disable_event().
>>
>> From below test results on 3 machines(2 ARM and one x86), time
>> consumed by EHCI interrupt handler droped much without performance
>> loss.
>>
>> 1 test description
>> 1.1 mass storage performance test:
>> - run below command 10 times and compute the average performance
>>
>>     dd if=/dev/sdN iflag=direct of=/dev/null bs=200M count=1
>
> It would be nice to get worst case numbers. How bad does it get
> if you reduce the sg size in usb-storage from 120K to 4K?

A quick test on one arm A15 box shows that the average speed over
10 times 'dd' becomes 8.0MB/sec from 8.160MB/sec when 'bs'
parameter of 'dd' changes to 4K, so there is ~1.9% performance
loss with the patch under the worst case.

Same test on my T410(x86), the speed difference is only 40K.

I will collect the worst case numbers and include it in the commit
log of V3.

Thanks,
--
Ming Lei