Probe Response packets sometimes delayed by 200ms

Michal Kazior michal.kazior at
Thu Oct 2 23:10:46 PDT 2014

On 3 October 2014 07:48, Avery Pennarun <apenwarr at> wrote:
> Hi all,
> We're chasing a problem where, with an ath10k device running as access
> point and a Macbook Air as a client, responses to probe requests are
> sometimes missed by the Macbook Air because they are delayed for a
> long time, and the Macbook has changed channels by the time they come
> through.
> ath10k driver version: from backports as of kvalo/ath-next on
> 2014-03-08 (v3.15-rc1-237-gd9bc4b9)
> Firmware version: 10.1.467.3
> Steps:
> - start capturing packets, either on the ath10k AP itself or a
> secondary monitor system
> - on the Macbook Air (which has joined your SSID at least once
> before), open and close the wifi dropdown menu a few times.  (May also
> happen with clients other than Macbook Air; not heavily tested.)

Was the Macbook Air disconnected cleanly on the AP?

There's a tx credit starvation bug which blocks wmi commands after
disassoc+deauth frames are queued (via wmi as well) and aren't acked
by station in which case wmi peer delete command times out and
sta_state splats a calltrace in kernel logs. This effectively leaves
firmware thinking the peer is still connected and it is never
disconnected (you can expect spurious sta kickout events after an hour
once that happens). This could explain why ath10k AP tries to play
powersave with the Macbook Air.

Or perhaps this is related to uAPSD? Do you have it enabled in
hostapd? Is Macbook Air associating with uAPSD enabled?

Or maybe firmwar expects host driver should reset some ap-sta
powersave related settings before deleting peer entries.

I don't have any other ideas now.


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