On Sun, 2011-02-13 at 09:56 -0800, Nathaniel J. Smith wrote: > We maintain several ring buffers that queue up packets for the > hardware to transmit. These buffers can be quite large, and the > quality of wireless connections can vary greatly; as a result, it can > be that a full queue might take multiple seconds to drain. > > For instance, if there is a high-bandwidth outgoing flow, like a large > file upload, then it will completely fill the tx queues. Once the > queues are full, then any other outgoing packets -- like those sent > when a user clicks on an HTTP link, or types into an SSH session -- > will have to wait at the end of the line, and will not actually be > transmitted until multiple seconds have passed. This results in a > suboptimal level of interactive response. > > So we really don't want to allow too many packets to get queued up. On > the other hand, we do want to queue up *some* packets, to maintain > throughput -- and the queue size that maintains interactivity for a > degraded 1 Mb/s connection might not be so great for some > super-fancy 802.11n 600 Mb/s connection. > > This patch estimates how long it takes the hardware to transmit one > packet (by comparing each packet's queue residency time to the number > of packets it had to wait behind), and then further smooths these > estimates with an EWMA. Then, it uses the estimated packet > transmission time to choose the maximum queue size that will still > produce reasonably bounded queue residency times, given current > conditions. This sounds nice -- but couldn't it just as well be implemented in mac80211, at least for most devices (that have accurate TX status reporting)? johannes -- 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
