Re: [PATCH rtw-next 3/4] wifi: rtw88: Set AMPDU factor to hardware

[Bitterblue Smith <rtl8821cerfe2@gmail.com>]

On 18/03/2025 04:06, Ping-Ke Shih wrote:
> Bitterblue Smith <rtl8821cerfe2@gmail.com> wrote:
>> On 17/03/2025 05:01, Ping-Ke Shih wrote:
>>> Bitterblue Smith <rtl8821cerfe2@gmail.com> wrote:
>>>>
>>>> Tell the chip the maximum AMPDU size supported by the AP. This greatly
>>>> improves the TX speed of RTL8814AU in the 2.4 GHz band. Before: ~90
>>>> Mbps. After: ~300 Mbps.
>>>>
>>>> Add this configuration for all the chips, even if it only has an effect
>>>> on RTL8814AU in my tests. Surely they all need this.
>>>
>>> The hardware default value of REG_AMPDU_MAX_LENGTH is 0xffff (unlimited)
>>> for most chips. It seems like RTL8812A/RTL8821A are also exceptions, so
>>> at power on function they do
>>>     rtw_write32(rtwdev, REG_AMPDU_MAX_LENGTH, 0xffffffff);
>>>
>>> I feel RTL8814A has similar setting, so maybe you can just add similar
>>> stuff.
>>>
>>> By the way, the AMPDU is controlled by TX descriptor basically:
>>>       pkt_info->ampdu_factor = ampdu_factor;
>>>       pkt_info->ampdu_density = ampdu_density;
>>>       pkt_info->ampdu_en = ampdu_en;
>>>
>>> Since you didn't change this part at all, I still feel setting
>>> REG_AMPDU_MAX_LENGTH to 0xffffffff can fix low throughput problem.
>>>
>>
>> I tried 0xffffffff just now and it doesn't work. It's the same with
>> both of my routers. They advertise a maximum AMPDU size of 64 K.
>> I can't just set it to 0xffff either, because then the upload speed
>> in the 5 GHz band suffers a lot. The dual band router advertises a
>> maximum AMPDU size of 256 K in the 5 GHz band so it gets a value of
>> 0x3ffff.
> 
> Not sure if 0xffffffff is a special value. Since this is a limit of
> AMPDU length, you can set a constant large value such as 0x3ffff you 
> have tested. Is there special case it can't handle?
> 
> 

0x3ffff is not good for the 2.4 GHz band. The upload is only ~90 Mbps
with both of the routers I tested. Same with 0x1ffff. Only 0xffff
works well for them.

0xffff is too little for the 5 GHz band. The upload speed is ~200 Mbps
less than with 0x3ffff.

I guess if you really don't want this patch I can hardcode 0xffff and
0x3ffff in rtw8814a_switch_band(). I just don't know if all access
points will be happy with that.