linux-kernel - Re: Sierra Wireless (MC8780) HSDPA speed issue

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Date:	Sun, 15 Mar 2009 21:33:59 -0700
From:	Greg KH <greg@...ah.com>
To:	Rory Filer <rfiler@...rraWireless.com>
Cc:	Ralf Nyren <ralf@...en.net>,
	Stephen Clark <sclark46@...thlink.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kevin Lloyd <klloyd@...rrawireless.com>
Subject: 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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