Re: [Madwifi-devel] WEP performance
Status: Beta
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From: Stephane L. <ste...@co...> - 2003-08-31 15:45:32
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Th WEP encryption is actually performed by the hardware. I cannot think of any reason why the ieee80211_wep_crypt() function exists. It doesn't seem to be called in normal operations. In any case, the performance hit is due to how the IV is set in driver/if_ath.c:ath_tx_start(). It calls get_random_bytes() for each IV, and on my system, that call takes 100ms. With the attached patch, performance is back to normal. get_random_bytes() is called only for the first IV, which is incremented thereafter. Stephane Peter Antypas wrote: > Hi all. > > This may not be the first time that you've heard this. It's about WEP > performance with this driver. > > When in (b) mode, performance drops to less than 1/4 of the unencrypted > mode. Using a LinkSys 802.11b AP, throughput goes from 525 KB/s to 96 > KB/s with no other variable other than turning WEP on/off. In (g) mode, > using a DLink 624 AP, I go from 1.2 MB/s to 740 KB/s which is almost > half. In both cases, the stationary computer is WIRED to the AP to leave > the band open for the wireless node. > > I have looked into the WEP encryption code in if_ieee80211subr.c and I > don't see anything that strikes me as terribly inefficient. I have > compared it to the linux-wlan code and it looks similar enough, save for > the fact that they use a statically defined CRC table, while the madwifi > driver initializes it (once, I hope). > > So what could be causing this? I don't have a lot of experience in > kernel land, but I would be willing to dig my hands into it if you can > provide some pointers. Anyone care to comment? Sam? > > Peter > > Hi-Fi through Wi-Fi > =============== > www.joyfaktory.com <http://www.joyfaktory.com> > > |