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

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Date:	Mon, 16 Mar 2009 13:48:02 +0100 (CET)
From:	Ralf Nyren <ralf@...en.net>
To:	Greg KH <greg@...ah.com>
cc:	Rory Filer <rfiler@...rraWireless.com>,
	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

Thanks Rory,

I have tried changing OBUFSIZE in ppp_async.c (still kernel 2.6.28.7), first
512 and then 4096. However the speed "limit" of about 100KB/s remains the same.
So perhaps there's some setup/firmware issue with the hardware. If I understand
things correctly the Windows driver uses a proprietary protocol to init the card
while in Linux you use the AT command interface. Could be something there which
makes a difference I guess.

Best regards, Ralf

On Sun, 15 Mar 2009, Greg KH wrote:

> 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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