Date: Wed, 30 Nov 2011 08:59:45 -0500 From: "Viet-Ha Pham" <hapvbk@yahoo.co.uk> To: "Bernhard Schmidt" <bschmidt@freebsd.org> Cc: freebsd-net@freebsd.org, Adrian Chadd <adrian@freebsd.org> Subject: Re: Wifi throughput test issue (FreeBSD 8.2) Message-ID: <5939430EC6AF43B79CB9BE99940E9B91@PC> In-Reply-To: <CAAgh0_Ym0Np4Py-aaxH=bEJcSJPAKcx2CFECMtgSD=%2B%2BVhUvLQ@mail.gmail.com> References: <69C75F6ECC9646C79374299EDF0E4304@PC> <CAAgh0_Ym0Np4Py-aaxH=bEJcSJPAKcx2CFECMtgSD=%2B%2BVhUvLQ@mail.gmail.com>
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Hi Bernhard, Thanks so much for your quick reply. I did not test this scenario with 9.0 or later so I don't have any idea if it's working ok or not. I'll do it next. For the debug options, I'll can do it right away and get back with more infor. HAPV -----Original Message----- From: Bernhard Schmidt Sent: Wednesday, November 30, 2011 8:34 AM To: Viet-Ha Pham Cc: freebsd-net@freebsd.org ; Adrian Chadd Subject: Re: Wifi throughput test issue (FreeBSD 8.2) On Wed, Nov 30, 2011 at 13:37, Viet-Ha Pham <hapvbk@yahoo.co.uk> wrote: > Hello, > > > I am doing some throughput measurement for Wifi network. I am using > jperf/iperf to generate traffic (at the transmitter) and measure the > throughput (at the receiver). The transmitter and receiver are running > FreeBSD 8.2, using CM9-GP as the Wifi NIC. We are testing AWGN channel. > So, the transmitter and receiver are connected by cables, txpower on both > sides is set lower than the max (ranging from 0 to 10), AWGN noise is > injected in the middle of the cable. > > We measure the maximum throughput at each transmission rate. Transmitter > is a STA, receiver is an AP. We fix the unicast rate at the transmitter to > 54 Mbps (using "ifconfig ... ucastrate" command). The packet size is set > to 400 Bytes, UDP protocol is used and the transmit bandwidth is set to 30 > Mbps in order to flood the transmission channel (to push it to its limit). > At first, at the receiver (AP) the measured throughput is about 12 Mbps. > Then I fix the unicast rate at the receiver (using ifconfig again) to 54 > Mbps. The measured throughput increases to 20 Mbps. I set the unicast rate > at the receiver to autoselect again, the throughput is still 20 Mbps. > > When I switch the rate at the receiver, there are multiple message > displayed on the screen of the transmitter: "wlan0: > ieee80211_new_state_locked: pending RUN -> AUTH transition lost". This > message is repeated for many times (at least 20). > > I repeated the test with all transmission rates, change the packet size > and still observe the same thing: a throughput improvement of about 30% is > observed when I switch the unicast rate at the receiver and the > improvement is still there when I switch the unicast rate back to > autoselect. The same thing is observed in modes a and g. The same thing is > observed if the unicast rate at the receiver is set different from the > unicast rate at the transmitter. > > > > I spent time to look at the kernel source codes but I did not find a solid > answer for this. Please help me to identify the problem and the answer. > > > My question is: > > 1. Why do I have that throughput improvement when I switch the rate like > that? > 2. Is it a bug in the driver? I think so, the driver might ignore/do some fancy stuff with a fixed ucastrate. @Adrian, do you know if ath_rate_sample has some debug options in that regard? > 3. What does the error/infor message on the transmitter mean? It might mean a lot of things, you should probably enable additional debug options to get a clue about what's going on. Btw, do you also see that behavior on HEAD (or at least the latest 9.x release/rc)? -- Bernhard
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