Re: b43 reduced performance in Linux-2.6.25

[Gautam Iyer <gi1242@stanford.edu>]

[-- Attachment #1: Type: text/plain, Size: 2423 bytes --]

On Tue, Apr 29, 2008 at 05:34:54PM -0500, Larry Finger wrote:

>> I saw a few threads about reduced performance in b43 in the 2.6.24 /
>> 2.6.25_rcXX kernels, but couldn't manage to fix the problem myself:
>> On my system, using ndiswrapper and the windows drivers gives me about
>> 1.5 times the performance of the in kernel b43 drivers.
>> Here are my system specs:
>>     Broadcom Corporation BCM4312 802.11a/b/g [14e4:4312] (rev 02)
>>     Linux 2.6.25 (gentoo-sources-2.6.25-r1).
>>     b43 wireless driver with firmware 410.2160 (2007-05-26 15:32:10)
>> I measured the performance by running "ttcp" between my Laptop and my
>> router. Using b43 on my Laptop gives about 2MB/s reported, and using
>> ndiswrapper gives me about 3MB/s under exactly the same situations.
>> Any ideas about what's going on? (I would be happy to provide you with
>> any further specs on my computer).
>
> Yes. Broadcom wrote the Windows drivers, but never gave the
> specifications to anyone else. Obvious those specs from their
> engineers are better than those from the _reverse_ engineers for your
> card. On my BCM4311/2 I get better throughput with the b43 driver than
> I get when running Windows. I _NEVER_ use ndiswrapper. Now that b43
> works, why would I want to taint my kernel?

I just moved to a different network and compared the performance between
b43 and ndiswrapper. They are now *almost* identical (both 2.5MB/s). I'd
even say that b43 sometimes performs slightly (50KB/s) better on
average! (GO LINUX WIRELESS!)

Looking at my syslog shows that on my home network (where b43 performed
50% worse), I find the following messages just after association:

    wlan0: switched to short barker preamble (BSSID=00:14:a5:0c:17:dc)
    wlan0: WMM queue=2 aci=0 acm=0 aifs=3 cWmin=15 cWmax=1023 burst=0
    wlan0: WMM queue=3 aci=1 acm=0 aifs=7 cWmin=15 cWmax=1023 burst=0
    wlan0: WMM queue=1 aci=2 acm=0 aifs=2 cWmin=7 cWmax=15 burst=30
    wlan0: WMM queue=0 aci=3 acm=0 aifs=2 cWmin=3 cWmax=7 burst=15

I don't find these messages when I connect on campus (and get the high
performance). So maybe the performance loss is WMM related.

My home router is of course running Linux (OpenWRT), so maybe I can
tweak the WMM parameters of the router to match what b43 is happy with!

Any suggestions,

Thanks again for your help!

GI

-- 
'Pessimist' -- Optimist with experience.

[-- Attachment #2: Type: application/pgp-signature, Size: 197 bytes --]