Hi!
> > > Hm, the 50% make me curious... have to look what's happening...
> >
> > For PL-2301/2302 devices, "ifconfig up" is mostly just posting a bulk read.
> > True with both "usbnet" and its (now obsolete) predecessor drivers "plusb"
> > and (for different devices) "net1080".
> >
> > Laplink-style cables can often support another mode (poll via USB "interrupts",
> > and then issue reads only when data is available) but not every device can work
> > that way (like, I seem to recall, an iPaq PDA). And that'd increase the latency
> > per packet by a couple milliseconds, even when it's possible.
>
> I thought that it is a dangling bulk read, but I have to check why it is
> still consuming PCI bandwidth, even without transmitting data...
As a datapoint, it does not consume PCI with JE's uhci. [Is it possible that
control transfers are being done and you turn FSBR on on control xfer?]
> > > > (running more than 4 times slower than normally. Ouch).
> > >
> > > Blame Intel. Either low latency or low PCI usage, you can choose...
> >
> > This problem is UHCI-specific, not USB-generic, yes?
> > Doesn't happen with OHCI?
>
> UHCI runs its descriptor chain only once a millisecond, which is bad, if you
> use breadth access mode to provide fair bandwith. Then each transfer can
> only get one TD (64byte) in one millisecond through. To avoid that, the
> bandwith reclamation is used, a nice word for a design/concept flaw, it
> simply loops the descriptor chain. That causes a high PCI load, even with no
> transfers in-progress, the descriptors are always read via PCI.
> Unfortunately, there's no delay-TD or such...
Would it be possible not to make loop, but to chain 16 TDs instead? 16 TDs
mean 1KB, 1KB per milisecond is more than enough?
About delay-TD idea: would it be possible to make low-speed transmit
to nonexisting device? That should delay it just well :-).
Pavel
--
Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.
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