Re: [Make-wifi-fast] [RFC/RFT 5/5] ath9k: Count RX airtime in airtime deficit

[Michal Kazior <michal.kazior@tieto.com>]

On 10 June 2016 at 11:08, Toke Høiland-Jørgensen <toke@toke.dk> wrote:
> Michal Kazior <michal.kazior@tieto.com> writes:
>
>> For A-MPDU all MPDU rx status (except last one) should share the same
>> timestamp. Last one has a different one so all you need is to
>> distinguish first and last MPDU. Non A-MPDU obviously are special case
>> (status bits are pricky).
>
> Right. So comparing the rs_stamp between first and last MPDU should give
> the duration of the entire thing?

Depends on how you define your "thing" :) I no, I don't know what
you'll actually measure. It should be reasonable either way.


> This would require keeping state
> between subsequent calls to the RX handler. Also, what happens if the
> last MPDU is lost?

No idea. If that's possible, then track last MPDU within PPDU, so you
can at least fallback to _something_ when you detect a new first
(A-)MPDU?

Or maybe it's impossible (i.e. not worth worrying) and HW always
reports last MPDU as far as status bits are concerned (regardless of
it being _actual_ last MPDU, i.e. it just says "ok, I'm done with this
PPDU").


>>> Is the entire A-MPDU received before the RX handler is called for the
>>> first frame?
>>
>> No idea. Maybe it is as there's distinction between "more" and
>> "moreaggr".
>
> Hmm. If it is, comparing the stamp of the first MPDU to the current time
> (when handling it) should give the needed duration? Will try doing that
> and see what the result is.

I'd say it's a little racy/inaccurate (and perhaps unreliable) to
compare any kind of global timer and compare it against your rx-status
descriptors.


Michał