Re: [PATCH 5/8] mac80211: A-MPDU Rx handling aggregation reordering

Ron Rindjunsky
2007-12-20T12:32:54Z

> > This patch handles the reordering of the Rx A-MPDU.
>
> I thought about this a bit more, here's a counter-proposal. :)
>
> Your current patch means that when a monitor mode interface is up, it
> will receive frames twice because the A-MPDU frames have already passed
> __ieee80211_rx() when they were sent up by the hardware, and that copies
> the frame to the monitor first thing.

true, i forgot monitor is no longer a handle like it used to be, and i
do pass there twice. this can be fixed by checking .ordered field
there

> Also, what you're doing means that
> the frame is accounted for channel load twice (yeah, I know, the stats
> there suck... but still...)

here i am already checking the .ordered field (like i proposed for
monitor), and ignore the in-order frames.

>
> What we'd really want I think is to
> (1) put the frame to monitor regularly [indicating A-MPDU in the
> radiotap header, this will need radiotap standard work, so not now]
> (2) "keep" the frame in the ieee80211_rx_h_reorder_ampdu rx-pre-handler
> (3) "release" the frame with an appropriate status later
>
> Hence, I think it'd be best to first reorganise the current code:
> (1) split __ieee80211_rx() right after the pre handler invocation and
> call e.g. __ieee80211_rx_handlers() which contains all the code
> from "if (sta && !(sta->flags & (WLAN_STA_WDS | WLAN_STA_ASSOC_AP"
> to "} else dev_kfree_skb(skb);"
> The function would have certain requirements like a filled
> ieee80211_txrx_data and running under rcu_read_lock().
> (2) then, you don't need status.ordered but can drop the frame right
> away or pass it to __ieee80211_rx_handlers().
>
> That way, we guarantee that each frame only passes through the complete
> RX path once and your dropping the unordered frames is equivalent to the
> reorder_ampdu handler having an oracle that tells it which frames to

so you suggest to remove ieee80211_rx_h_reorder_ampdu in favor of a
function that will call ieee80211_sta_manage_reorder_buf?
in any case, function or handler, i think it is better to leave this
separation - filtering and reordering - in 2 different place.

> drop and which to keep :)
>
> Comments?
>

I looked at your proposal, generally it can be done, yet there are
pros and cons we need to consider:
1 - (con) by inserting the .ordered check to ieee80211_rx_monitor or
before it i can avoid changing the code - just 2 more lines and
problem is solved
2 - (pro) yet, i'll end up checking the .ordered field in 3 places -
monitor,statistics and reordering buf, which lowers the encapsulation
of work inside ieee80211_rx_h_reorder_ampdu
3 - (con) i will have to free un-needed sk_buffs in
ieee80211_sta_stop_rx_BA_session without going back to __ieee80211_rx,
which may confuse othere.
4 - (pro) i'll use less variables (with a little more code, but a clear one)

> johannes
>
>