[linux-elitists] USB-Serial and pppd

Greg KH greg@kroah.com
Thu Jun 12 10:09:35 PDT 2008

On Thu, Jun 12, 2008 at 02:27:55AM -0400, Greg Folkert wrote:
> Ok this one has been itching for a while.
> I have an (sierra.ko supported) PCMCIA Slot AC595 EVDO RevA Cellular
> Broadband card for use with my Verizon service. $65 a
> month/"unlimited" (fine print claims "unlimited" == 5GiB/month)
> Now, I use this card in a couple of different machines.
> Machine #1 == Lenovo T61 (6465CTO) T7500 processor, 4GB RAM all Intel
> Chipset, 200GB disk...etc; Dual Boot WindowsXP and Debian Sid updated
> nearly daily
> Machine #2 == Dell Insirion 8000 850MHz, 512MB RAM, various chipsets
> included. Single Boot Ubuntu 8.04.
> I cannot get anything above 512KiB/sec D/L while in Linux on either
> machine.
> While in Windows on #1, I get upwards of 2MiB/sec, from the same
> location... just rebooting to it with the card in it.
> Reboot a second time back into Linux... 512KiB/sec.
> Yes, I've gone at length through pppd's options and config files... 
> (with or without)921600, compression options out the whing-whang, proper
> LCP settings for my provider, crtscts, auth, allthatjazzandabagofchips
> I've google'd, Y!'d, MSN'd, Asked Jeeves, Tried to get answers.com,
> explored the Amazon.com, relied on Wikipedia, Dogpiled on the search,
> Called on Zuula.com Dawn, saw the clusty.com-fsck, looked in vain for
> Alta-vista, Did the AOLSEARCH METOO, hit the HOTBOT-ten, tried to
> looksmart, didn't have a gigablast, Found Live... DEAD, discovered Lycos
> after Death but came up empty handed, tried direction from DMOZ and
> finally check alltheweb.

But you never asked the driver author now did you :)

If so, he would tell you exactly what is wrong (hint, it's the driver,
not pppd)...

Use the latest kernel versions, it is a much faster driver than the
older ones.  If you still have performance issues, let me know and I'll
show you how to tweak it to go even faster...

> I've read there that usb-serial is known to be slow (and you keep having
> to repeat yourself)... but that Sierra seems to require it and in fact
> seems to get in the way. 

It requires it for the "core" but not for the throughput issues.

> So, what exactly am I missing? I know I've probably glazed over it and I
> apologize in advance for re-hashing this again for the umpteenth time.
> (a quote from a response by g. k-h to someone else recently):
> The generic usb serial driver is KNOWN TO BE A VERY SLOW DRIVER!
> ...
> The code was not designed to be fast, only get the job done.

Yes, the "generic" usb-serial driver is slow, as designed.  The sierra
driver is not using the "generic" driver, but only the usb-serial
framework, and as such, should be much faster.

What kernel versions are you using in your above configurations?


greg k-h

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