On Thu, 26 Apr 2007 21:14:00 -0700, James Ketrenos wrote: > Right now the scanning in mac80211 is slow. I haven't really dug > into it to see if it will transition from passive to active if it > detects RF activity on an otherwise passive channel, etc. but I have > seen that if we turn on hw scanning we can get results back in a few > seconds vs. 10 or more. The scanning in mac80211 needs to be improved. I'd consider this as a job for user space MLME, though. > The more passive channels you add (most of 802.11a) the slower the > scanning gets. This seems to be a common, not a softmac specific problem. At least, if done properly, I don't see how there could be a difference in softmac vs. firmware scanning wrt. time. > If done right, the stack would set up the list of channels to scan, > whether to scan the channel active or passive, and the template for > the probe request to use. > > For sw based scans, the stack would then have a mechanism for > executing that scan through a series of tunes, transmits, etc. For > hw scans, it would pass that structure to the driver which would > package it for the hardware and pass it down. > > Upon completion of the scan (sw or hw) the notification would come > back to the stack to let it know scanning is complete. > > The sw scan engine would be tied into the rest of the transmit > infrastructure to manage off channel time, etc. (which you don't have > to do with hw scanning since the hardware/uCode does it all for you) This sounds reasonable and I think it addresses most of Michael's objections. Unfortunately, I don't see how user space MLME fits into this. Any idea how to solve this remaining issue? (But no ugly hacks, please.) > Unless there is a mechanism to quickly and easily toggle between > filter and don't filter, you'll end up turning off hw/uCode > filtering of packets all the time. I'm not sure I understand. What prevents you from turning off the filtering just during the scanning? > Which means the hardware would be set to full promiscuous mode and > every packet Rx'd would get tossed to the host to then either process > or discard--which keeps the host CPU awake (which isn't good on > laptops or anywhere else folks care about power consumption) And > scanning is one of those things that happens more frequently when you > are not plugged in and are moving around the home, school, office, > etc. Yes, power consumption is a good argument. However, how much time you spend in scanning (compared to the total time you use your wifi card)? It would be helpful to see some numbers. > > What's the big bottleneck that justifies moving this to > > hardware? > > With the 3945 its mainly power consumption. Do you have some numbers? Personally, I have no idea how much power you can save by offloading the scan. It could be interesting. Thanks, Jiri -- Jiri Benc SUSE Labs - To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
