Date: Wed, 1 Mar 2006 13:54:23 -0800
From: Greg KH <greg@kroah.com>
To: Ren? Rebe <rene@exactcode.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: MAX_USBFS_BUFFER_SIZE
Message-ID: <20060301215423.GA17825@kroah.com>
References: <200603012116.25869.rene@exactcode.de> <20060301213223.GA17270@kroah.com> <200603012242.35633.rene@exactcode.de>
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On Wed, Mar 01, 2006 at 10:42:35PM +0100, Ren? Rebe wrote:
> Hi,
> 
> On Wednesday 01 March 2006 22:32, Greg KH wrote:
> > On Wed, Mar 01, 2006 at 09:16:25PM +0100, Ren?? Rebe wrote:
> > > Hi,
> > > 
> > > I wonder if:
> > > 
> > > drivers/usb/core/devio.c:86
> > > #define MAX_USBFS_BUFFER_SIZE   16384
> > > 
> > > is some random, or outdated limit or if there really is some code path that could
> > > not handle bigger URBs.
> > > 
> > > For performance reasons I would like to use bigger packages for an image
> > > aquisition device.
> > 
> > Why not just send down 2 urbs with that size then, that would keep the
> > pipe quite full.
> 
> Because that requires even more modifications to libusb and sane (i_usb) ...

No, do it in your application I mean.

> So, queing alot URBs is the recommended way to sustain the bus? Allowing
> way bigger buffers will not be realistic?

16Kb is "way big" in the USB scheme of things aready.  Look at the size
of your endpoint.  It's probably _very_ small compared to that.  So no,
larger buffer sizes is not realistic at all.

thanks,

greg k-h
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