Felix Fietkau <nbd@xxxxxxxx> writes:
> On 2019-09-27 10:35, Toke Høiland-Jørgensen wrote:
>> Felix Fietkau <nbd@xxxxxxxx> writes:
>>> + switch (status->encoding) {
>>> + case RX_ENC_LEGACY:
>>> + if (WARN_ON_ONCE(status->band > NL80211_BAND_5GHZ))
>>> + return 0;
>>> +
>>> + sband = dev->hw->wiphy->bands[status->band];
>>> + if (!sband || status->rate_idx > sband->n_bitrates)
>>> + return 0;
>>> +
>>> + rate = &sband->bitrates[status->rate_idx];
>>> +
>>> + return mt76_calc_legacy_rate_duration(rate, sp, len);
>>> + case RX_ENC_VHT:
>>> + streams = status->nss;
>>> + idx = status->rate_idx;
>>> + group = VHT_GROUP_IDX(streams, sgi, bw);
>>> + break;
>>> + case RX_ENC_HT:
>>> + streams = ((status->rate_idx >> 3) & 3) + 1;
>>> + idx = status->rate_idx & 7;
>>> + group = HT_GROUP_IDX(streams, sgi, bw);
>>> + break;
>>> + default:
>>> + WARN_ON_ONCE(1);
>>> + return 0;
>>> + }
>>> +
>>> + if (WARN_ON_ONCE(streams > 4))
>>> + return 0;
>>> +
>>> + duration = airtime_mcs_groups[group].duration[idx];
>>> + duration <<= airtime_mcs_groups[group].shift;
>>> + duration *= len;
>>> + duration /= AVG_PKT_SIZE;
>>> + duration /= 1024;
>>
>> On an earlier patch of mine you expressed concern over divisions in the
>> fast path. Does this mean this is no longer a concern? Or is the
>> compiler doing fancy things with the constant division here? :)
> I made the constants power-of-2, so that the compiler can turn them into
> bit shifts. I verified the disassembly: no divisions left in the code.
I see. Neat :)
There's still a regular division in the legacy rate calc further up,
though, right? But I guess that doesn't happen so often?
-Toke
