linux-kernel - Re: rt61pci - bad performance

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Date:	Fri, 13 Aug 2010 10:35:39 +0200
From:	Helmut Schaa <helmut.schaa@...glemail.com>
To:	Andreas <andihartmann@...19freenet.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ivo van Doorn <IvDoorn@...il.com>,
	Gertjan van Wingerde <gwingerde@...il.com>,
	linux-wireless@...r.kernel.org
Subject: Re: rt61pci - bad performance

Hi Andreas,

Am Freitag 13 August 2010 schrieb Andrew Morton:
> (cc's added)
> 
> On Sun, 08 Aug 2010 11:49:49 +0200
> Andreas <andihartmann@...19freenet.de> wrote:

[...]

> > wlan0     IEEE 802.11bg  ESSID:"--------"
> >            Mode:Managed  Frequency:2.412 GHz  Access Point: some AP
> >            Bit Rate=1 Mb/s   Tx-Power=5 dBm
> >            Retry  long limit:7   RTS thr:off   Fragment thr:off
> >            Encryption key:off
> >            Power Management:off
> >            Link Quality=38/70  Signal level=-72 dBm
> >            Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
> >            Tx excessive retries:0  Invalid misc:0   Missed beacon:0
> > 
> > The throughput is measured with ping -f -s 7000 and xosview -n.

This doesn't look like an appropriate way to measure the throughput. You
should use something like iperf [1] or netperf [2] for your measurements
to get more accurate results.

> > If I'm using ndiswrapper with the windows driver, first of all, I can 
> > see additional information in iwconfig:
> > 
> > wlan0     IEEE 802.11g  ESSID:"--------"
> >            Mode:Managed  Frequency:2.412 GHz  Access Point: some AP
> >            Bit Rate=54 Mb/s   Tx-Power:20 dBm   Sensitivity=-121 dBm
> >            RTS thr=2347 B   Fragment thr=2346 B
> >            Encryption key:some key   Security mode:restricted
> >            Power Management:off
> >            Link Quality:62/100  Signal level:-56 dBm  Noise level:-96 dBm
> >            Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
> >            Tx excessive retries:0  Invalid misc:0   Missed beacon:0
> > 
> > 
> > There is a switch for sensitivity (which is not supported with rt61pci) 
> > and the link quality compared with ndiswrapper is worse (38% to 62%).

I wouldn't trust the link quality values that much, the calculation in rt61pi
is most likely different from what the windows driver does. So it is not
really comparable.

> > The following is remarkably too:
> > ndiswrapper uses a Tx-Power of 20 dBm, rt61pci only 5 dBm. I don't know, 
> > why rt61pci uses 5 dBm. It's a hard limit and I can't set it on a value 
> > higher than 5 unless the driver is patched. Nevertheless, setting a 
> > higher value (of 20 dBm) by patch does not mean to get a better performance.

Could you elaborate please? Did you actually try to patch it or is this just
an assumption?

> > Ndiswrapper shows an encryption key, rt61pci not. Does it mean, that 
> > rt61pci doesn't use hardware encryption?

hw crypto should be enabled by default in rt61pci, however, I don't know
if it is actually working ;)

> > With ndiswrapper, the rt61pci-chip achieves a throughput of 2,6 MBytes/s 
> > - that's about 1 MByte/s more than rt61pci.
> > 
> > I have to say, that the difference between rt61pci and ndiswrapper gets 
> > worse if the link quality is getting more badly. Or in other words: 
> > ndiswrapper handles bad connections better then rt61pci.
> > 
> > 
> > Do you have any idea to get rt61pci working as fast as ndiswrapper?

Please run proper measurements first and post the results again.

Thanks,
Helmut

[1] http://sourceforge.net/projects/iperf/
[2] http://www.netperf.org/
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