On Sat, Jan 28, 2012 at 12:09 PM, Marek Lindner <lindner_marek@xxxxxxxx> wrote: > On Sunday, January 29, 2012 04:03:41 you wrote: >> On Sat, Jan 28, 2012 at 11:58 AM, Marek Lindner <lindner_marek@xxxxxxxx> > wrote: >> > On Sunday, January 29, 2012 03:17:32 Daniel Halperin wrote: >> >> Adaptive RTS/CTS is important to control for interference---RTS/CTS is >> >> there so that other Wi-Fi devices know not to interfere with your >> >> flow. It may well be the case that this is not a major problem in >> >> whatever your scenario you're working, Marek, but it makes a big >> >> difference in a many bad corner cases. >> > >> > I am very well aware of what RTS/CTS is for and I am not against using >> > it. However, having the rate algorithm overriding the user setting for a >> > specific rate is extremely hard to grasp or debug. >> > To give you an understanding where I am coming from: In our networks we >> > experienced extremely variable throughput ranging from 30Mbit/s (single >> > stream) to 0.2 Mbit/s in the next second. As you can imagine we were >> > trying to figure out what was going on. After spending some time and >> > losing hair I noticed that the RTS/CTS implementation of our driver >> > (ath9k) is buggy. Every once in a while the nodes would "battle" each >> > other with RTS/CTS packets. Strange enough for us, sometimes no RTS >> > packets were sent and sometimes they would battle. All attempts to >> > disable RTS/CTS for the mere sake of testing(!) was impossible. First I >> > thought ath9k did not properly implement the "iw rts" setting but that >> > wasn't the case. After losing more hair I realized that minstrel_ht, a >> > rate control algorithm(!), was overriding my rts settings but not >> > always(!). The only way to make RTS shut up was to apply the posted >> > patch. >> >> Can you explain what the low-level behavior of an RTS/CTS "battle" is? >> >> Abstractly, the behavior you're describing sounds like a buggy driver >> that doesn't obey overheard RTS or CTS packets. > > I certainly can explain it but this is for another thread and unrelated to the > points raised before. Frankly, the correctness of your argument depend on whether there's a bug or not. If the difference is -2% normally and +300% in bad interference conditions, you're going to lose this debate. If the difference is legitimately -99% normally, you might win. Your description reminds me of this: http://www.spinics.net/lists/linux-wireless/msg83803.html. Maybe there really is a bug in ath9k. Dan -- 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
