On Mon, Feb 8, 2016 at 3:56 PM, Emmanuel Grumbach <egrumbach@xxxxxxxxx> wrote: > On Mon, Feb 8, 2016 at 11:54 AM, Krishna Chaitanya > <chaitanya.mgit@xxxxxxxxx> wrote: >> On Mon, Feb 8, 2016 at 2:56 PM, Emmanuel Grumbach <egrumbach@xxxxxxxxx> wrote: >>> On Mon, Feb 8, 2016 at 10:38 AM, Felix Fietkau <nbd@xxxxxxxxxxx> wrote: >>>> Requires software tx queueing support. frag_list support (for zero-copy) >>>> is optional. >>>> >>>> Signed-off-by: Felix Fietkau <nbd@xxxxxxxxxxx> >>>> --- >>> >>> >>> Ok - looks fine, but... and here comes the hard stuff. >>> The frame size in the PLCP is limited in a way that you can't - from a >>> spec POV - enable A-MSDU for low rates. Of course, you don't want to >>> do that for low rates at all regardless of the spec. >>> Since you build the A-MSDU in the mac80211 Tx queue which is not aware >>> of the link quality, how do we prevent A-MSDU if the rate is low / >>> dropping. >>> I'd even argue that when the rates get lower, you'll have more >>> packets piling up in the software queue and ... even more chance to >>> get A-MSDU in the exact case where you really want to avoid it? >> >> Similar to triggering AMPDU setup, we should put this control >> in RC (minstrel) to start/stop AMSDU based on link quality/if the rates >> drop below a pre-defined MCS (or) only for best-throughput rates. > > Ok - but the size of A-MPDU is determined in the firmware / hardware > typically (at least for Intel devices and I have to admit my ignorance > about other designs...). So that if you get bad link conditions, the > firmware can play for that size. A-MSDU built in the host is a > different story. I remember that athXk devices attach the rate on the > Tx packet itself so that the rate control is serialized with the data > path. > iwlwifi works differently: we have a map of rates in the firmware. > This map is maintained in the driver updated based on the feedback we > get from the device. When an update is needed, iwlwifi sends a command > to the firmware and that command bypasses all the Tx packets currently > queue so that a packet that is already waiting in the queue will be > sent with the updated map. This allows iwlwifi to react downgrade > faster when needed. > So - for athXk (and maybe the MediaTek devices Felix is working on), > this may not be a big problem: you'd need to add another input to the > A-MSDU building code coming from the rate control. > FWIW: in iwlwifi I simply decided to be on the safe side and allowed > the driver to build A-MSDUs only if the rate is fairly high and we are > not downgrading. But you saw (and commented on) that patch already I > think :) Yes, this approach is going to be tough for those devices with HW RC. We might need something like amsdu_action to get some feedback from device about using of amsdu? -- 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
