netdev - Re: RTL8723BE performance regression

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Date:   Wed, 2 May 2018 05:58:42 +0000
From:   Pkshih <pkshih@...ltek.com>
To:     "jprvita@...il.com" <jprvita@...il.com>,
        "Larry.Finger@...inger.net" <Larry.Finger@...inger.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jprvita@...lessm.com" <jprvita@...lessm.com>,
        Birming Chiu <birming@...ltek.com>,
        "drake@...lessm.com" <drake@...lessm.com>,
        Chaoming_Li <chaoming_li@...lsil.com.cn>,
        "kvalo@...eaurora.org" <kvalo@...eaurora.org>,
        莊彥宣 <yhchuang@...ltek.com>,
        "derosier@...il.com" <derosier@...il.com>,
        Steven Ting <steventing@...ltek.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux@...lessm.com" <linux@...lessm.com>,
        Shaofu <shaofu@...ltek.com>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
Subject: Re: RTL8723BE performance regression

On Wed, 2018-05-02 at 05:44 +0000, Pkshih wrote:
> 
> > -----Original Message-----
> > From: João Paulo Rechi Vita [mailto:jprvita@...il.com]
> > Sent: Wednesday, May 02, 2018 6:41 AM
> > To: Larry Finger
> > Cc: Steve deRosier; 莊彥宣; Pkshih; Birming Chiu; Shaofu; Steven Ting; Chaoming_Li; Kalle Valo;
> > linux-wireless; Network Development; LKML; Daniel Drake; João Paulo Rechi Vita; linux@...lessm.c
> om
> > Subject: Re: RTL8723BE performance regression
> > 
> > On Tue, Apr 3, 2018 at 7:51 PM, Larry Finger <Larry.Finger@...inger.net> wrote:
> > > On 04/03/2018 09:37 PM, João Paulo Rechi Vita wrote:
> > >>
> > >> On Tue, Apr 3, 2018 at 7:28 PM, Larry Finger <Larry.Finger@...inger.net>
> > >> wrote:
> > >>
> > >> (...)
> > >>
> > >>> As the antenna selection code changes affected your first bisection, do
> > >>> you
> > >>> have one of those HP laptops with only one antenna and the incorrect
> > >>> coding
> > >>> in the FUSE?
> > >>
> > >>
> > >> Yes, that is why I've been passing ant_sel=1 during my tests -- this
> > >> was needed to achieve a good performance in the past, before this
> > >> regression. I've also opened the laptop chassis and confirmed the
> > >> antenna cable is plugged to the connector labeled with "1" on the
> > >> card.
> > >>
> > >>> If so, please make sure that you still have the same signal
> > >>> strength for good and bad cases. I have tried to keep the driver and the
> > >>> btcoex code in sync, but there may be some combinations of antenna
> > >>> configuration and FUSE contents that cause the code to fail.
> > >>>
> > >>
> > >> What is the recommended way to monitor the signal strength?
> > >
> > >
> > > The btcoex code is developed for multiple platforms by a different group
> > > than the Linux driver. I think they made a change that caused ant_sel to
> > > switch from 1 to 2. At least numerous comments at
> > > github.com/lwfinger/rtlwifi_new claimed they needed to make that change.
> > >
> > > Mhy recommended method is to verify the wifi device name with "iw dev". Then
> > > using that device
> > >
> > > sudo iw dev <dev_name> scan | egrep "SSID|signal"
> > >
> > 
> > I have confirmed that the performance regression is indeed tied to
> > signal strength: on the good cases signal was between -16 and -8 dBm,
> > whereas in bad cases signal was always between -50 to - 40 dBm. I've
> > also switched to testing bandwidth in controlled LAN environment using
> > iperf3, as suggested by Steve deRosier, with the DUT being the only
> > machine connected to the 2.4 GHz radio and the machine running the
> > iperf3 server connected via ethernet.
> > 
> 
> We have new experimental results in commit af8a41cccf8f46 ("rtlwifi: cleanup 
> 8723be ant_sel definition"). You can use the above commit and do the same 
> experiments (with ant_sel=0, 1 and 2) in your side, and then share your results.
> Since performance is tied to signal strength, you can only share signal strength.
> 

Please pay attention to cold reboot once ant_sel is changed.