On Fri, Apr 1, 2011 at 5:21 PM, Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote: > On Fri, 2011-04-01 at 17:15 +0530, Vivek Natarajan wrote: >> In a highly noisy environment, since the driver could not send >> the packets out in 100ms, some applications stall and eventually >> fail as mac80211 stops the netdevice queues for flush when power >> save is triggered. Most of the WMM testcases fail in the Wifi >> testing because of this. >> Increasing the dynamic ps timeout to 200-300ms helps but in noisy >> channel conditions even if there is a continuous tx traffic, mac80211 >> tries to go into PS. The new implementation checks for any frames >> queued in the driver tx queues and based on that mac80211 decides >> to go for power save. This also prevents redundant stopping of >> netdevice queues which helps more applications to run properly. > > I think as an API change this needs more justification. Why does this > need a new callback, for example? Ideally the driver should enter power save only when there is no tx frame. When there are about 10 APs in the environment the tx rate of the driver drops and the application slows down since it has not yet received ACKs for the frames already queued in the hardware. Since this ACK may take more than 100ms, stopping the dev queues for entering PS at this stage breaks applications, WMM test case in my testing. If there are tx_frames already pending in the queue, postponing the PS logic helps to avoid redundant queue stops. Since, I could not find any other way in mac80211 to see if the driver has not completed the transmission of any frame, a new API to check for pending frames is used. When power save is enabled by default and in a noisy environment, this API certainly helps in improving the average throughput. Any other idea? Vivek. -- 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
