Re: [PATCH v2 1/2] mac80211: extend current rate control tx status API

Ben Greear
2022-03-10T16:44:01Z

On 3/10/22 8:07 AM, Thomas Hühn wrote:
> Hiho
>
>> On 9. Mar 2022, at 21:38, Ben Greear <greearb@candelatech.com> wrote:
>>
>> On 3/9/22 11:57 AM, Jonas Jelonek wrote:
>>> This patch adds the new struct ieee80211_rate_status and replaces
>>> 'struct rate_info *rate' in ieee80211_tx_status with pointer and length
>>> annotation.
>>> The struct ieee80211_rate_status allows to:
>>> (1) receive tx power status feedback for transmit power control (TPC)
>>> per packet or packet retry
>>> (2) dynamic mapping of wifi chip specific multi-rate retry (mrr)
>>> chains with different lengths
>>> (3) increase the limit of annotatable rate indices to support
>>> IEEE802.11ac rate sets and beyond
>>> ieee80211_tx_info, control and status buffer, and ieee80211_tx_rate
>>> cannot be used to achieve these goals due to fixed size limitations.
>>> Our new struct contains a struct rate_info to annotate the rate that was
>>> used, retry count of the rate and tx power. It is intended for all
>>> information related to RC and TPC that needs to be passed from driver to
>>> mac80211 and its RC/TPC algorithms like Minstrel_HT. It corresponds to
>>> one stage in an mrr. Multiple subsequent instances of this struct can be
>>> included in struct ieee80211_tx_status via a pointer and a length variable.
>>> Those instances can be allocated on-stack. The former reference to a single
>>> instance of struct rate_info is replaced with our new annotation.
>>> Further mandatory changes in status.c and mt76 driver due to the
>>> removal of 'struct rate_info *rate' are also included.
>>> status.c already uses the information in ieee80211_tx_status->rate in
>>> radiotap, this is now changed to use ieee80211_rate_status->rate_idx.
>>> mt76 driver already uses struct rate_info to pass the tx rate to status
>>> path. It is now enclosed in an instance of struct ieee80211_rate_status
>>> with default values for retry_count and tx_power. The latter should be
>>> adjusted later to pass more accurate values.
>>> Compile-Tested: current wireless-next tree with all flags on
>>> Tested-on: Xiaomi 4A Gigabit (MediaTek MT7603E, MT7612E) with OpenWrt
>>> Linux 5.10.83
>>> Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
>>> ---
>>> drivers/net/wireless/mediatek/mt76/tx.c | 13 +++-
>>> include/net/mac80211.h | 10 ++-
>>> net/mac80211/status.c | 91 ++++++++++++++-----------
>>> 3 files changed, 71 insertions(+), 43 deletions(-)
>>> diff --git a/drivers/net/wireless/mediatek/mt76/tx.c b/drivers/net/wireless/mediatek/mt76/tx.c
>>> index 6b8c9dc80542..ed3f3654999f 100644
>>> --- a/drivers/net/wireless/mediatek/mt76/tx.c
>>> +++ b/drivers/net/wireless/mediatek/mt76/tx.c
>>> @@ -62,13 +62,20 @@ mt76_tx_status_unlock(struct mt76_dev *dev, struct sk_buff_head *list)
>>> };
>>> struct mt76_tx_cb *cb = mt76_tx_skb_cb(skb);
>>> struct mt76_wcid *wcid;
>>> + struct ieee80211_rate_status rate = {0};
>>> wcid = rcu_dereference(dev->wcid[cb->wcid]);
>>> if (wcid) {
>>> status.sta = wcid_to_sta(wcid);
>>> -
>>> - if (status.sta)
>>> - status.rate = &wcid->rate;
>>> + if (status.sta) {
>>> + rate.rate_idx = wcid->rate;
>>> + rate.retry_count = 1;
>>> + /* Default 0 for now, can be used by TPC algorithm */
>>> + rate.tx_power = 0;
>>> +
>>> + status.rates = &rate;
>>> + status.n_rates = 1;
>>> + }
>>> }
>>> hw = mt76_tx_status_get_hw(dev, skb);
>>> diff --git a/include/net/mac80211.h b/include/net/mac80211.h
>>> index c50221d7e82c..1e98ed04b446 100644
>>> --- a/include/net/mac80211.h
>>> +++ b/include/net/mac80211.h
>>> @@ -1131,6 +1131,12 @@ ieee80211_info_get_tx_time_est(struct ieee80211_tx_info *info)
>>> return info->tx_time_est << 2;
>>> }
>>> +struct ieee80211_rate_status {
>>> + struct rate_info rate_idx;
>>> + u8 retry_count;
>>> + s8 tx_power;
>>> +};
>>
>> Please document the units for tx_power. Many chips can support 1/2 db increments, for instance,
>> so consider that for units... A zero txpower is still a valid number, so you probably need
>> something other than 0 to be the 'default'. Like -128?
>
> Certain 802.11a/g/n Atheros chips provide a 0,5dB tx-power step granularity, while Mediatek 802.11ac chips have 1dB or even 3dB step width. So I would argue that a 1dB step width is a good compromise as the common value for new tpc algorithms.

If you use 0.5db units for that struct, then it will support anything with that granularity or higher.
But, fine with me if you want to just have it be 1db units.

>
> The ath9k chips I have used so far support a minimum tx-power of -5dBm (=0,32mW), Mediatek has a min of 0dBm (=1mW)… so I would argue to use 0dBm (=1mW) as common minimum tx-power value, as the any possible spatial reuse gain happens from 0dBm up to max tx-power.

If a chip supports setting to txpower to -5, then why not let the API support that? Have The value -128
be 'do not set', and anything else will mean 'try to set the chip to this power or the nearest thing to it
that the chip supports'.

Thanks,
Ben

>
>>
>> And, does 'retry_count' actually mean 'try_count'? So a single tx would be retry_count = 1?
>> Please document that as well.
>>
>> Thanks,
>> Ben
>
> Greetings Thomas
>

--
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc http://www.candelatech.com