Re: [RFC PATCH v7] rtl8xxxu: Improve TX performance of RTL8723BU on rtl8xxxu driver

[Kalle Valo <kvalo@codeaurora.org>]

Jes Sorensen <jes.sorensen@gmail.com> writes:

> On 8/5/19 9:14 AM, Chris Chiu wrote:
>> We have 3 laptops which connect the wifi by the same RTL8723BU.
>> The PCI VID/PID of the wifi chip is 10EC:B720 which is supported.
>> They have the same problem with the in-kernel rtl8xxxu driver, the
>> iperf (as a client to an ethernet-connected server) gets ~1Mbps.
>> Nevertheless, the signal strength is reported as around -40dBm,
>> which is quite good. From the wireshark capture, the tx rate for each
>> data and qos data packet is only 1Mbps. Compare to the Realtek driver
>> at https://github.com/lwfinger/rtl8723bu, the same iperf test gets
>> ~12Mbps or better. The signal strength is reported similarly around
>> -40dBm. That's why we want to improve.
>> 
>> After reading the source code of the rtl8xxxu driver and Realtek's, the
>> major difference is that Realtek's driver has a watchdog which will keep
>> monitoring the signal quality and updating the rate mask just like the
>> rtl8xxxu_gen2_update_rate_mask() does if signal quality changes.
>> And this kind of watchdog also exists in rtlwifi driver of some specific
>> chips, ex rtl8192ee, rtl8188ee, rtl8723ae, rtl8821ae...etc. They have
>> the same member function named dm_watchdog and will invoke the
>> corresponding dm_refresh_rate_adaptive_mask to adjust the tx rate
>> mask.
>> 
>> With this commit, the tx rate of each data and qos data packet will
>> be 39Mbps (MCS4) with the 0xF00000 as the tx rate mask. The 20th bit
>> to 23th bit means MCS4 to MCS7. It means that the firmware still picks
>> the lowest rate from the rate mask and explains why the tx rate of
>> data and qos data is always lowest 1Mbps because the default rate mask
>> passed is always 0xFFFFFFF ranges from the basic CCK rate, OFDM rate,
>> and MCS rate. However, with Realtek's driver, the tx rate observed from
>> wireshark under the same condition is almost 65Mbps or 72Mbps, which
>> indicating that rtl8xxxu could still be further improved.
>> 
>> Signed-off-by: Chris Chiu <chiu@endlessm.com>
>> Reviewed-by: Daniel Drake <drake@endlessm.com>
>> ---
>
> Looks good to me! Nice work! I am actually very curious if this will
> improve performance 8192eu as well.
>
> Ideally I'd like to figure out how to make host controlled rates work,
> but in all my experiments with that, I never really got it to work well.
>
> Signed-off-by: Jes Sorensen <Jes.Sorensen@gmail.com>

This is marked as RFC so I'm not sure what's the plan. Should I apply
this?

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