[PATCH AUTOSEL 5.18 72/93] net/cdc_ncm: Increase NTB max RX/TX values to 64kb

Sasha Levin
2022-08-11T16:09:08Z

From: Łukasz Spintzyk <lukasz.spintzyk@synaptics.com>

[ Upstream commit 5588d628027092e66195097bdf6835ddf64418b3 ]

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>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220720060518.541-2-lukasz.spintzyk@synaptics.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 */
--
2.35.1