On 03/01/2023 10:13, Ping-Ke Shih wrote:
>
>> -----Original Message-----
>> From: Bitterblue Smith <rtl8821cerfe2@xxxxxxxxx>
>> Sent: Saturday, December 31, 2022 12:54 AM
>> To: linux-wireless@xxxxxxxxxxxxxxx
>> Cc: Jes Sorensen <Jes.Sorensen@xxxxxxxxx>; Ping-Ke Shih <pkshih@xxxxxxxxxxx>
>> Subject: [PATCH 2/2] wifi: rtl8xxxu: Use a longer retry limit of 48
>>
>> The Realtek rate control algorithm goes back and forth a lot between
>> the highest and the lowest rate it's allowed to use. This is due to
>> a lot of frames being dropped because the retry limits set by
>> IEEE80211_CONF_CHANGE_RETRY_LIMITS are too low. (Experimentally, they
>> are 4 for long frames and 7 for short frames.)
>>
>> The vendor drivers hardcode the value 48 for both retry limits (for
>> station mode), which makes dropped frames very rare and thus the rate
>> control is more stable.
>
> I have similar feeling with Realtek 802.11ac chips as well, but I didn't
> dig further years ago. Maybe, it could have TX EVM problem.
>
>>
>> Because most Realtek chips handle the rate control in the firmware,
>> which can't be modified, ignore the limits set by
>> IEEE80211_CONF_CHANGE_RETRY_LIMITS and use the value 48 (set during
>> chip initialisation), same as the vendor drivers.
>>
>> Fixes: 26f1fad29ad9 ("New driver: rtl8xxxu (mac80211)")
>
> No sure if "Fixes" is suitable to this patch, because original looks well but
> bad performance in real.
>
Mostly I care about the Fixes tag because it gets the patch into the
stable kernels, but I can use the Cc tag for that instead.
>> Signed-off-by: Bitterblue Smith <rtl8821cerfe2@xxxxxxxxx>
>
> Reviewed-by: Ping-Ke Shih <pkshih@xxxxxxxxxxx>
>
>> ---
>> drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c | 9 ---------
>> 1 file changed, 9 deletions(-)
>>
>> diff --git a/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
>> b/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
>> index f5fd3c448587..9bca5e837583 100644
>> --- a/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
>> +++ b/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
>> @@ -6184,7 +6184,6 @@ static int rtl8xxxu_config(struct ieee80211_hw *hw, u32 changed)
>> {
>> struct rtl8xxxu_priv *priv = hw->priv;
>> struct device *dev = &priv->udev->dev;
>> - u16 val16;
>> int ret = 0, channel;
>> bool ht40;
>>
>> @@ -6194,14 +6193,6 @@ static int rtl8xxxu_config(struct ieee80211_hw *hw, u32 changed)
>> __func__, hw->conf.chandef.chan->hw_value,
>> changed, hw->conf.chandef.width);
>>
>> - if (changed & IEEE80211_CONF_CHANGE_RETRY_LIMITS) {
>> - val16 = ((hw->conf.long_frame_max_tx_count <<
>> - RETRY_LIMIT_LONG_SHIFT) & RETRY_LIMIT_LONG_MASK) |
>> - ((hw->conf.short_frame_max_tx_count <<
>> - RETRY_LIMIT_SHORT_SHIFT) & RETRY_LIMIT_SHORT_MASK);
>> - rtl8xxxu_write16(priv, REG_RETRY_LIMIT, val16);
>> - }
>> -
>> if (changed & IEEE80211_CONF_CHANGE_CHANNEL) {
>> switch (hw->conf.chandef.width) {
>> case NL80211_CHAN_WIDTH_20_NOHT:
>> --
>> 2.38.0
>>
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