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Date:   Mon, 18 Jul 2022 16:40:59 +0200
From:   Greg KH <>
To:     Łukasz Spintzyk <>
Subject: Re: [PATCH v3 2/2] net/cdc_ncm: Increase NTB max RX/TX values to 64kb

On Mon, Jul 18, 2022 at 02:36:18PM +0200, Łukasz Spintzyk wrote:
> DisplayLink ethernet devices require NTB buffers larger then 32kb
> in order to run with highest performance.
> This patch is changing upper limit of the rx and tx buffers.
> Those buffers are initialized with CDC_NCM_NTB_DEF_SIZE_RX and
> CDC_NCM_NTB_DEF_SIZE_TX which is 16kb so by default no device is
> affected by increased limit.
> Rx and tx buffer is increased under two conditions:
>  - Device need to advertise that it supports higher buffer size in
>    dwNtbMaxInMaxSize and dwNtbMaxOutMaxSize.
>  - cdc_ncm/rx_max and cdc_ncm/tx_max driver parameters must be adjusted
>    with udev rule or ethtool.
> Summary of testing and performance results:
> Tests were performed on following devices:
>  - DisplayLink DL-3xxx family device
>  - DisplayLink DL-6xxx family device
>  - ASUS USB-C2500 2.5G USB3 ethernet adapter
>  - Plugable USB3 1G USB3 ethernet adapter
>  - EDIMAX EU-4307 USB-C ethernet adapter
>  - Dell DBQBCBC064 USB-C ethernet adapter
> Performance measurements were done with:
>  - iperf3 between two linux boxes
>  - instance running on local test machine
> Insights from tests results:
>  - All except one from third party usb adapters were not affected by
>    increased buffer size to their advertised dwNtbOutMaxSize and
>    dwNtbInMaxSize.
>    Devices were generally reaching 912-940Mbps both download and upload.
>    Only EDIMAX adapter experienced decreased download size from
>    929Mbps to 827Mbps with iper3, with openspeedtest decrease was from
>    968Mbps to 886Mbps.
>  - DisplayLink DL-3xxx family devices experienced performance increase
>    with iperf3 download from 300Mbps to 870Mbps and
>    upload from 782Mbps to 844Mbps.
>    With openspeedtest download increased from 556Mbps to 873Mbps
>    and upload from 727Mbps to 973Mbps
>  - DiplayLink DL-6xxx family devices are not affected by
>    increased buffer size.
> Signed-off-by: Łukasz Spintzyk <>
> ---
>  v3: No new changes to v2 2/2.
>  It is just rebase on top of changed v3 1/2 patch

Any reason you dropped my reviewed-by?

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