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

[Jes Sorensen]

On 9/17/19 3:40 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@xxxxxxxxxxxx>
> Reviewed-by: Daniel Drake <drake@xxxxxxxxxxxx>

I am still traveling after Plumbers and don't have my 8723bu dongles
with me, but I'd say this looks good.

Acked-by: Jes Sorensen <Jes.Sorensen@xxxxxxxxx>

Jes