Big USB speed difference when compiled as module (was Re: speed difference between using hard-linked and modular drives?)

Big USB speed difference when compiled as module (was Re: speed difference between using hard-linked and modular drives?)

[Tim Pepper]

On Thu 08 Nov at 17:01:24 +0100 roy@karlsbakk.net done said:
> 
> Are there any speed difference between hard-linked device drivers and
> their modular counterparts?

I've been wondering this as well.  I've got a curious situation:  With usbcore
and the uhci driver compiled into the kernel I can initiate transfers to a usb
device I have (Creative Nomad Jukebox) at what I'm eyeballing to be near the
12Mbps USB speed.  These tranfers always fail.  With both drivers compiled as
modules the transfers are over an order of magnitude slower, not even
appearing to reach the 1.5Mbps USB speed, but they succeed.  I haven't had a
chance to try to figure out what's going on for sure.

It's been a little while since I was playing with this but I believe I saw
the same thing with the usb-uhci driver as well but it didn't seem to like
talking to the Nomad regardless of it being compiled as a module or not.
This was with the 2.4.13 kernel.  I can provide more details upon request.

BTW: is there a way to do USB sniffing in software in linux?  I'd imagine it's
possible, but just can't find anything that does...


Tim

Re: Big USB speed difference when compiled as module (was Re: speed difference between using hard-linked and modular drives?)

[Johannes Erdfelt]

On Thu, Nov 08, 2001, Tim Pepper <tpepper@vato.org> wrote:
> On Thu 08 Nov at 17:01:24 +0100 roy@karlsbakk.net done said:
> > 
> > Are there any speed difference between hard-linked device drivers and
> > their modular counterparts?
> 
> I've been wondering this as well.  I've got a curious situation:  With usbcore
> and the uhci driver compiled into the kernel I can initiate transfers to a usb
> device I have (Creative Nomad Jukebox) at what I'm eyeballing to be near the
> 12Mbps USB speed.  These tranfers always fail.  With both drivers compiled as
> modules the transfers are over an order of magnitude slower, not even
> appearing to reach the 1.5Mbps USB speed, but they succeed.  I haven't had a
> chance to try to figure out what's going on for sure.
> 
> It's been a little while since I was playing with this but I believe I saw
> the same thing with the usb-uhci driver as well but it didn't seem to like
> talking to the Nomad regardless of it being compiled as a module or not.
> This was with the 2.4.13 kernel.  I can provide more details upon request.

This absolutely should not be the result of compiling into the kernel.
It's most likely a bug in the HC which just happened to show up with
modules.

> BTW: is there a way to do USB sniffing in software in linux?  I'd imagine it's
> possible, but just can't find anything that does...

Not in Linux yet.

JE

Re: Big USB speed difference when compiled as module (was Re: speed difference between using hard-linked and modular drives?)

[Greg KH]

On Thu, Nov 08, 2001 at 02:24:12PM -0800, Tim Pepper wrote:
> BTW: is there a way to do USB sniffing in software in linux?  I'd imagine it's
> possible, but just can't find anything that does...

There was a patch on the linux-usb-devel list a few months ago that
contained a patch to do this.  You might check the archives if you're
interested.

thanks,

greg k-h