Re: [PATCH v2 2/2] net/cdc_ncm: Increase NTB max RX/TX values to 64kb

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jul 14, 2022 at 02:02:17PM +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
>  - http://openspeedtest.com/ 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 <lukasz.spintzyk@synaptics.com>
> ---
> 
> v2:
>  - Information how to change tx,rx buffer size
>  - Added performance tests results to the commit description.
> 
> 
>  include/linux/usb/cdc_ncm.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/usb/cdc_ncm.h b/include/linux/usb/cdc_ncm.h
> index f7cb3ddce7fb..2d207cb4837d 100644
> --- a/include/linux/usb/cdc_ncm.h
> +++ b/include/linux/usb/cdc_ncm.h
> @@ -53,8 +53,8 @@
>  #define USB_CDC_NCM_NDP32_LENGTH_MIN		0x20
>  
>  /* Maximum NTB length */
> -#define	CDC_NCM_NTB_MAX_SIZE_TX			32768	/* bytes */
> -#define	CDC_NCM_NTB_MAX_SIZE_RX			32768	/* bytes */
> +#define	CDC_NCM_NTB_MAX_SIZE_TX			65536	/* bytes */
> +#define	CDC_NCM_NTB_MAX_SIZE_RX			65536	/* bytes */
>  
>  /* Initial NTB length */
>  #define	CDC_NCM_NTB_DEF_SIZE_TX			16384	/* bytes */
> -- 
> 2.36.1
> 

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Thanks for the additional information in the changelog text.