Re: [Make-wifi-fast] [PATCH v6 2/4] mac80211: Import airtime calculation code from mt76

[Johannes Berg <johannes@sipsolutions.net>]

On Wed, 2019-10-23 at 11:59 +0200, Toke Høiland-Jørgensen wrote:
> From: Toke Høiland-Jørgensen <toke@redhat.com>
> 
> Felix recently added code to calculate airtime of packets to the mt76
> driver. Import this into mac80211 so we can use it for airtime queue limit
> calculations later.
> 
> The airtime.c file is copied verbatim from the mt76 driver, and adjusted to
> use mac80211 data structures instead (which is fairly straight forward).
> The per-rate TX rate calculation is split out to its own
> function (ieee80211_calc_tx_airtime_rate()) so it can be used directly for
> the AQL calculations added in a subsequent patch.

Any way it could be exposed by mac80211 back to the drivers, perhaps, to
share it?

> The only thing that it was not possible to port directly was the bit that
> read the internal driver flags of struct ieee80211_rate to determine
> whether a rate is using CCK or OFDM encoding. Instead, just look at the
> rate index, since at least mt76 and ath10k both seem to have the same
> number of CCK rates (4) in their tables.

This is highly questionable ...

> +	switch (status->encoding) {
> +	case RX_ENC_LEGACY:
> +		if (WARN_ON_ONCE(status->band > NL80211_BAND_5GHZ))
> +			return 0;
> +
> +		sband = hw->wiphy->bands[status->band];
> +		if (!sband || status->rate_idx > sband->n_bitrates)
> +			return 0;
> +
> +		rate = &sband->bitrates[status->rate_idx];
> +		cck = (status->rate_idx < CCK_NUM_RATES);

Why not

	cck = rate->flags & IEEE80211_RATE_MANDATORY_B;

I mean .. we know that IEEE80211_RATE_MANDATORY_B rates are exactly the
CCK rates, and that's not really going to change?

Alternatively, we could do

	cck = sband->band == NL80211_BAND_2GHZ &&
	      !(rate->flags & IEEE80211_RATE_ERP_G);

or even

	cck = rate->bitrate == 10 || rate->bitrate == 20 ||
	      rate->bitrate == 55 || rate->bitrate == 110;

:)

> +	default:
> +		WARN_ON_ONCE(1);

You can't do that in mac80211 either. That might be fine for mt76, but
mac80211 already supports HE.

johannes