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From:   =?UTF-8?B?6YKx5ZCN56Kp?= <ccchiu77@gmail.com>
Date:   Thu, 20 May 2021 09:28:46 +0800
Message-ID: <CANgQ54cKA5N1h1kMgS52N1acrp+pJzV3e+8vd61miSS0_VVD7Q@mail.gmail.com>
Subject: Re: How does the rate adaptive mask work on Realtek WiFi driver
To:     Pkshih <pkshih@realtek.com>
Cc:     Andy Huang <tehuang@realtek.com>,
        "Larry.Finger@lwfinger.net" <Larry.Finger@lwfinger.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "kvalo@codeaurora.org" <kvalo@codeaurora.org>,
        Reto Schneider <reto.schneider@husqvarnagroup.com>,
        "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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Pkshih <pkshih@realtek.com> =E6=96=BC 2021=E5=B9=B45=E6=9C=8814=E6=97=A5 =
=E9=80=B1=E4=BA=94 =E4=B8=8B=E5=8D=882:08=E5=AF=AB=E9=81=93=EF=BC=9A
>
>
> > -----Original Message-----
> > From: =E9=82=B1=E5=90=8D=E7=A2=A9 [mailto:ccchiu77@gmail.com]
> > Sent: Monday, May 10, 2021 4:36 PM
> > To: Pkshih; Andy Huang; Larry.Finger@lwfinger.net; kuba@kernel.org; kva=
lo@codeaurora.org; Reto
> > Schneider; linux-wireless@vger.kernel.org; linux-kernel@vger.kernel.org
> > Subject: How does the rate adaptive mask work on Realtek WiFi driver
> >
> > Hi guys,
> >     I had a problem while verifying the ampdu tx throughput with the
> > rtl8xxxu driver on RTL8188CUS module. The throughput number is
> > relatively good, 39~42Mbps  TCP on 2.4GHz channel. However, the
> > retransmission rate is high, it's 15% ~ 21% with rtl8xxxu driver and
> > It's almost the same result with the rtl8192cu driver. I can get
> > averagely 7~10% retransmission rate in the same test bed with Realtek
> > vendor driver.
> >
> >     From the air capture, I can see the rtl8xxxu driver keep sending
> > the aggregated frames in MCS7 and doesn't even fall back to lower MCS
> > index in the subsequent retries. I can only see very few retried
> > packets been sent with MCS0 or 6Mbps grate. On the vendor driver, I'll
> > see the retried ampdu packets with MCS4 after 3 retries w/o ack from
> > the receiver.
> >
> >     From the rate mask command issued by the h2c command, I force both
> > the rtl8xxxu driver and vendor driver to use the same ratemask 0xfffff
> > (MCS 0-7 and b/g rate included) and leave the arg0 as-is (mostly 0xa0)
> > and I expect both drivers can do the rate adaptive thing in the same
> > way, but it seems to make no difference. The rtl8xxxu driver still
> > sends the packets with highest MCS.
> >
> >     Can anyone tell me what should I expect the rate adaptive to work
> > with the rate mask 0xfffff and 0xf0000? Does the 0xf0000 means that it
> > will pick up a tx rate only between nrate MCS4 to MCS7? I need a base
> > line so that I can judge it's simply a rate mask problem or maybe the
> > h2c command is not written correctly. Please kindly suggest what I
> > should do next. Thanks
> >
>
> The rate mask indicates which rates will be used by rate adaptive mechani=
sm.
> I'm not sure the exact bit allocation for CCK/OFDM/MCS, maybe
> 0x0000f/0x00ff0/0xff0000 for CCK/OFDM/MCS respectively, but you can trace
> vendor driver to know the detail.
>
> I suggest you can try to send only OFDM rate mask, and expect to see OFDM
> rate only by your sniffer. If it's still keep on MCS7, rate adaptive may
> not work properly.
>
Thanks. That's my expectation and I'll try to verify it on vendor
driver and upstream rtl8192cu driver.

> Also, you can compare the content of rate adaptive H2C with vendor driver=
 to
> see if the format is correct.
>
> Another thing is to try 'fix_rate' in tx_desc. Check the vendor driver to
> know the use_rate/rate/bw fields of tx_desc. Then, try to fix the rate yo=
u
> want.
>
If I set the fix_rate in tx_desc, will the rate mask in H2C command be
ignored? Or the underlying firmware will do the tx rate fallback for
the retry packets?

Chris

> --
> Ping-Ke
>