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

[Chris Chiu]

On Thu, May 30, 2019 at 2:22 AM Larry Finger <Larry.Finger@xxxxxxxxxxxx> wrote:
>
> 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.

Thanks. I'll modify this in next revision.

> >
> > 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@xxxxxxxxxxxx>
>
> I have not tested this patch, but I plan to soon.
>
> Larry
>
>