On Wed, 13 Nov 2002, David Brownell wrote:
> Sounds like your CDC hardware isn't as fast as your CATC hardware, or
> else the CDC code is doing some strange things to slow transfers down.
> You're getting half the throughput you should get on 10BaseT!
^^^^^^^^^^^^^^^^^^^
Dave, you're so close to a big question nobody's asked yet =)
Brad, do you have any indicators on the hub or the device on whether
you're full-duplex or half-duplex? Any kernel messages?
Just my two bits, as a former network-running-geek. I can't count the
number of times i've cursed poorly made cables for only giving half-duplex
signal 50m from the hub... (fluorescent bulbs are not my friends.)
[leadup snipped]
> It's easy to understand if you focus on short network packets, maybe
> ones that just take two full speed USB packets: with queueing, you can
> exchange nine (and a half) such network packets per frame, else it's just
> one per frame. (Or at high speed they'd take part of one bulk packet,
> forty per microframe versus just one...) For bigger packets there's a
> smaller win, though at higher speeds (100BaseT full duplex over USB 2.0!)
> the difference will be significant even for big packets.
>
Maybe (hah) i'm showing my ignorance here, but why not simply pass flags
and callback to the lower level, and have it call you with its own
completeed URBs, doing its own queueing? This is very nice, in that we
should never block IO (although blocking IO is highly beneficial when
you're running out of memory for URBs a delinquent driver isn't
processing...).
The reason i ask is that there's a lot of tuning to be done in a system
structured like this, and tuning is annoying. Especially if there's a
chance of getting the computer to do it for us.
--
/jbm, but you can call me Josh. Really, you can!
"What's a metaphor?" "For sheep to graze in"
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