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

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Date:	Sun, 22 Nov 2009 11:14:28 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Simon Arlott <simon@...e.lp0.eu>
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 Sun, 22 Nov 2009, Simon Arlott wrote:

> 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():

You mean usb_hcd_poll_rh_status().

>         /* 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.

It shouldn't make any difference; that timer is used with OHCI only in 
exceptional circumstances (like immediately after a device is plugged 
in or unplugged), not during normal operation.  But maybe something 
strange is going on.  You could add a printk in ohci_hub_status_data(), 
which is the routine that timer ends up calling.

Alan Stern

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