On Mon, Feb 14, 2011 at 04:56, Nathaniel J. Smith <njs@xxxxxxxxx> wrote: > I have an iwl3945 in my laptop, and find that whenever I saturate the > outgoing connection -- which happens daily when my rsync backup kicks > in -- then latency becomes astronomical (what Jim Gettys calls > "bufferbloat"). I've measured 12-13 second ping times to my router. As > you can imagine, this makes web browsing or interactive SSH somewhat > uncomfortable. For those who aren't aware of this, more info: http://gettys.wordpress.com/2010/12/03/introducing-the-criminal-mastermind-bufferbloat/ Re-(re-)stating the issue in question: When a network link is congested, packets are being buffered for a "long" time in an attempt to not drop any traffic; despite almost all protocols being either built on TCP or designed to deal with packet loss. This causes latency issues as the sender is not receiving any indication that the network is congested and hence continuing to send as fast as it can, filling these buffers and causing high latencies as they are emptied out over the congested link. The short term solution (but not an overall solution by any means) is to reduce these buffers so that packets are dropped when links are congested. > This patch series teaches the driver to measure the average rate of > packet transmission for each tx queue, and adjusts the queue size > dynamically in an attempt to achieve ~2 ms of added latency. IMHO, I'm not sure that this is the best method of implementing this solution: most wireless (and ethernet) devices have some form of buffer for the same reason, so implementing a solution for iwlwifi is not an overall solution - we need some method of doing this for *all* network devices, not just iwlwifi. That said, your reasoning for the queue management simplification seems sound - but as I don't know the iwlwifi code so I can't really comment on it any further than that. Finally, your numbers are damn impressive, and this is the first attempt that I'm aware of to solve this problem. Thanks, -- Julian Calaby Email: julian.calaby@xxxxxxxxx Profile: http://www.google.com/profiles/julian.calaby/ .Plan: http://sites.google.com/site/juliancalaby/ -- 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
