linux-kernel - Re: cxacru usb_bulk_msg() firmware upload 36x slower with OHCI vs. UHCI

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Message-ID: <4B09196D.7040107@simon.arlott.org.uk>
Date:	Sun, 22 Nov 2009 10:58:53 +0000
From:	Simon Arlott <simon@...e.lp0.eu>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: cxacru usb_bulk_msg() firmware upload 36x slower with OHCI vs.
 UHCI

On 18/11/09 22:25, Alan Stern wrote:
> On Wed, 18 Nov 2009, Simon Arlott wrote:
>> > What happens with other sorts of devices, such as a USB flash drive?
>>  
>> I can write a 10MB file to an USB flash drive over OHCI, and umount+sync
>> takes around 13 seconds.
> 
> Yes, that's about right.  It leads me to wonder if something funny is
> going on with the device, or least with the firmware-loading part of
> it.  Odd that it works differently with UHCI and OHCI, though.  There
> shouldn't be any differences visible to the device.  You don't have
> anything else attached to the same bus, do you?

Yes, but not in use and I could disconnect everything to test it.

core/hcd.c has an interesting comment in usb_hcd_check_unlink_urb():
        /* The USB 2.0 spec says 256 ms.  This is close enough and won't
         * exceed that limit if HZ is 100. The math is more clunky than
         * maybe expected, this is to make sure that all timers for USB devices
         * fire at the same time to give the CPU a break inbetween */

I'll try increasing the frequency of this timer too.

-- 
Simon Arlott
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