Re: speeding up ugen by an order of magnitude.

On Wed, 7 Jul 2004, M. Warner Losh wrote:

> In message: <Pine.BSF.4.21.0407071137440.80217-100000_at_InterJet.elischer.org>
>             Julian Elischer <julian_at_elischer.org> writes:
> : > Nevertheless I see ugen more as a quick and dirty way to test drive a
> : > device from userland with all it's great debugging capabilities before
> : > writing a specific kernel driver.
> : > The requirement that ugen has to be generic is often bad for
> : > performance sensitive applications.
> : 
> : Ugen is used in production all over the place where people have to used
> : devices there is no specific support for, and where there is no
> : kernel expertise.
> 
> usb drivers are very easy to write.  I think that making it easier to
> write those drivers is going to be better for the project in the long
> run.
> 
> ugen is supposed to be general.  If we can make it faster w/o
> sacrificying this generalness, that's OK.  But if we can't, then you
> gotta do stuff in the kernel.  That's always been the case (and why we
> don't have userland tcp, for example).  Some things have to be in the
> kernel to be fast.

I don't think this has to sacrifice generalness..

Matt Dillon just made a simple patch for this on Dfly and I'm looking at
back-porting it. there is nothing in ugen that shouldn't let it take
data from a bulk USB2 device at a good speed except that it doesn't ask
for the data that fast.. it is possible that there is a problem in the
ehci driver too, but I haven't got my mind around that driver quite
fully enough yet to say for sure.. it looks like it doesn't allow more
than one transfer per msec frame from the ugen device.  solving this
would allow the use of smaller buffers. I don;t think it's a problem
woth overhead and small transfers, but rather that ugen is asking for
only 1 x 1KB transaction per mSec when USB2 is capable of delivering
60KB/mSec. I think increasing the buffer size means still asking for one
transaction per mSec, but it's a bigger transaction :-)



> 
> Warner
>