Re: pvusb performance

[Noboru Iwamatsu <n_iwamatsu@jp.fujitsu.com>]

James,

> My pvUSB windows driver is now working at a very basic level (flash
> memory stick), and I'm conscious of the fact that I only send one
> request on the ring at a time and have to wait for it to complete before
> I can put the next one on. Can this be improved?

Possible.
RING accepts two or more requests, and queued requests are sent to
backend at a time.

> I think maybe it can't with your current usbback driver - there would
> need to be some mechanism to flush the ring of all subsequent requests
> in the case of an error, eg when I get a 'Read 65536 bytes' request from
> Windows, I do this:
> 
> . Put read request command on ring
> . Wait for response
> . Put data request on ring for first 512 bytes
> . Wait for response
> . Put data request on ring for next 512 bytes
> . etc
> . etc
> 
> If there is a buffer underrun, I can see no way for Linux to do
> something with the subsequent data requests... it would need to do
> something like put the ring into a error/underrun condition and 'eat'
> all the requests until a clear error request came down the ring.
> 
> Or maybe this is already part of the design?

Current pvusb doesn't care it.

You mean, when error occurred, HCD has to be responsible for flushing
the subsequent requests?

Should urb transferring errors be handled with USB device drivers
(the upper layer of HCD)?

If urb unlinking work properly, would it be solved?


Noboru.