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From: Hans Petter Selasky <hselasky@c2i.net>
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Date: Fri, 26 Jan 2007 18:03:27 +0100
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Cc: cperciva@freebsd.org, "M. Warner Losh" <imp@bsdimp.com>,
	current@freebsd.org
Subject: Re: Interesting speed benchmarks
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On Friday 26 January 2007 17:28, M. Warner Losh wrote:
> In message: <45B99A59.6070902@freebsd.org>
>
>             Colin Percival <cperciva@freebsd.org> writes:
> : M. Warner Losh wrote:
> : > In message: <45B9895B.9020709@freebsd.org>
> : >
> : >             Colin Percival <cperciva@freebsd.org> writes:
> : > : M. Warner Losh wrote:
> : > : > Firewire does around 40MB/s, while USB 2.0 maxes out at about
> : > : > 12MB/s.
> : > :
> : > : I get 25MB/s from my Vantec Nexstar3
> : > : USB 2.0 enclosure:
> : > :
> : > : http://www.daemonology.net/blog/2006-01-28-vantex-nexstar3.html
> : >
> : > Still, 25MB/s is no 40MB/s...
> :
> : Sure, but it means that the performance issues aren't simply a global
> : "USB 2.0 is bad".  What does `diskinfo -c` say about your firewire and
> : USB interfaces?
>

>
> I haven't tested the Hans Petter Selasky usb stack to see if it is any
> better.  It appears there's no scatter gather there, so that might
> make the numbers even worse.  But if the command queueing is better,
> then it might make up for it.

Yes, it has scatter and gather since August last year :-) But all USB drivers 
currently use copy-in/copy-out to/from the DMA buffer. With regard to "umass" 
there is one copy-out/copy-in per transfer. Currently all transfers are done 
in bulks of 131072 bytes, so there is not too much overhead.

I am considering direct buffer loading.

--HPS