On Tue, Feb 24, 2015 at 2:26 AM, Jouni Malinen <j@xxxxx> wrote: > On Tue, Feb 24, 2015 at 01:29:27PM +1100, Andrew McGregor wrote: >> Over the weekend I found a bug in minstrel-ht that might well be >> implicated here. >> >> The last retransmit rate is meant to be a 'get the packet there >> reliably' rate; minstrel-ht doesn't do that right, and can pick a >> fairly flaky rate instead. >> >> Can't generate a proper patch right now, so this diff might not apply >> cleanly, but the fix is simply to change 75 to 99 in the two places >> below: > > While this may indeed be helpful, I don't think it is sufficient for > this EAPOL frame related issue. What I would like to see is minstrel_ht > using a basic rate (something non-HT) at the end of the retry series for > EAPOL frames. > > The current behavior looks very suspicious to me. The early EAPOL frames > after association are being used to probe for higher rates. This results > in the total number of retry attempts actually getting smaller than any > other frame, i.e., minstrel_ht seems to be using significantly _less_ > robust choices for the EAPOL frames than following "normal" data frames! > This should really be the other way around.. > > As an example, I'm seeing this on 5 GHz band (with the 75 to 99 change > in place, but behavior was more or less identical without it): > - the first EAPOL frame (msg 2/4) getting one attempt at MCS 3, 2 > attempts at MCS 0, 2 attempts at MCS 0 (yes, identical to the previous > one) with total maximum of 5 attempts > - the second EAPOL frame (msg 4/4) getting one attempt at MCS 9, 2 > attempts at MCS 0, 2 attempts at MCS 0 with total maximum of 5 > attempts > - another data frame after this: 5 attempts at MCS 9, 5 attempts at MCS > 3, 5 attempts at MCS 3 with total maximum of 15 attempts(!!) I would in general prefer that the excessive retries in the present driver layers in wifi be dramatically reduced, the packet dropped and the problem punted to higher layers. > This cannot be the best approach here.. Falling back faster to the lowest possible rate with minimum retries, and then giving up sooner would be better. 15 attempts? jeeze.... > For the > IEEE80211_TX_CTRL_PORT_CTRL_PROTO cases, there are identified issues > where failing to deliver the frame results is significant issues either > in getting connected in the first place or getting disconnected if > rekeying fails. > > I'm not sure how this would be implemented cleanly in minstrel_ht or > whether that is even the best place (i.e., rate.c could do this > instead), but I'd like that third attempt for control port cases to be > dropped to use a (lowish) basic rate and non-MCS at that since there may > be some interop issues with HT MCS early during association. > Alternatively with drivers like ath9k that support 4 rate values, it > would also be fine to add this basic rate attempt (or well, I'd have > multiple, say 4, such attempts) as an additional 4th entry which does > not currently seem to get used with minstrel at all. > > The "(lowish) basic rate" here could be defined as 6 Mbps OFDM for 5 GHz > band and either that or maybe even 2 Mbps or 5.5 Mbps on 2.4 GHz (if > included by the AP in basic rate set). > > -- > Jouni Malinen PGP id EFC895FA > _______________________________________________ > ath9k-devel mailing list > ath9k-devel@xxxxxxxxxxxxxxx > https://lists.ath9k.org/mailman/listinfo/ath9k-devel -- Dave Täht Let's make wifi fast, less jittery and reliable again! https://plus.google.com/u/0/107942175615993706558/posts/TVX3o84jjmb -- 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
