linux-kernel - Re: [RFC PATCH v3] rtl8xxxu: Improve TX performance of RTL8723BU on rtl8xxxu driver

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Date:   Wed, 29 May 2019 13:22:23 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Chris Chiu <chiu@...lessm.com>, jes.sorensen@...il.com,
        kvalo@...eaurora.org, davem@...emloft.net
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...lessm.com
Subject: Re: [RFC PATCH v3] rtl8xxxu: Improve TX performance of RTL8723BU on
 rtl8xxxu driver

On 5/29/19 12:03 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 driver from
> https://github.com/lwfinger/rtl8723bu, the same iperf test gets ~12
> Mbps or more. The signal strength is reported similarly around
> -40dBm. That's why we want to improve.

The driver at GitHub was written by Realtek. I only published it in a prominent 
location, and fix it for kernel API changes. I would say "the Realtek driver at 
https://...", and every mention of "Larry's driver" should say "Realtek's 
driver". That attribution is more correct.
> 
> After reading the source code of the rtl8xxxu driver and Larry's, the
> major difference is that Larry'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 Larry's driver, the tx rate observed from
> wireshark under the same condition is almost 65Mbps or 72Mbps.
> 
> I believe the firmware of RTL8723BU may need fix. And I think we
> can still bring in the dm_watchdog as rtlwifi to improve from the
> driver side. Please leave precious comments for my commits and
> suggest what I can do better. Or suggest if there's any better idea
> to fix this. Thanks.
> 
> Signed-off-by: Chris Chiu <chiu@...lessm.com>

I have not tested this patch, but I plan to soon.

Larry