Re: Sierra Wireless (MC8780) HSDPA speed issue

On Sun, Mar 15, 2009 at 03:30:54PM -0700, Rory Filer wrote:
Hi Ralf

Using the driver we sent you on a call-box (i.e. with a "perfect"
simulated network connection) on Ubuntu 8.04 we were seeing ~4 Mbps on
the downlink. So I would rule out any problem with the driver and
conclude it must be something in either PPP/Linux or in the modem. In
order to rule out the modem, I've got a question into one of our UMTS
engineers and will send you a reply when we get the answer.

We did play around a little with 2.4 kernels of Linux and discovered
there is a buffer in PPP_ASYNC.C which, when its size is increased,
doubled the throughput. If you are savvy enough with Linux, you might
want to try playing with that. We stopped short of any thorough
testing of changing this array size, but were pleased with the result.
If I recall properly, the size of this array is (was, in 2.4) 256
bytes. Doubling it gave an immediate improvement. We were guessing
that the small size of this buffer was fine in the "old days" when
modems peaked at ~56 kbps. Even 8 years ago that was the fastest you
could go with a GPRS product, now our new HSPA+ products yields 21
Mbps on Telstra's network! Quite a difference.

Ah, the OBUFSIZE #define in drivers/net/ppp_async.c?

Anyone care to bump this size up and see if that helps out?

thanks,

greg k-h
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