DFU upload speed through BT SMP is slow

Question

DFU file upload speed through BT SMP is painstakingly slow especially for Matter firmware with MCUboot which are about 800 kB. 
 I just simply compiled and provisioned Matter lamp example on nRF52840 DK and without modifications the upload speed was around 1.5 kB/s from iPhone 14. 
 After the following modifications (suggested here ): 
 BT_L2CAP_TX_MTU=498 
 BT_BUF_ACL_TX_SIZE=251 
 BT_BUF_ACL_RX_SIZE=502 
 BT_CTLR_DATA_LENGTH_MAX=251 
 it became 3.7 kB/s. It's better but still much slower that I would expect. Is it possible to improve it a bit more?

JamesDougherty · Accepted Answer

Hello, 
 I just got done working on ours and it seems OK. I've tested from our Android app and it transfers the, almost 500 kB image, in about 35 seconds. We are using the nRF52840 SoC and the nRF21540 FEM on our boards. 
 What other config options are you using? One of the main ones is: 
 CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU=y 
 as that will imply the: 
 NCS_SAMPLE_MCUMGR_BT_OTA_DFU_SPEEDUP 
 config. The NCS_SAMPLE_MCUMGR_BT_OTA_DFU_SPEEDUP will set all of those for you: 
 config NCS_SAMPLE_MCUMGR_BT_OTA_DFU_SPEEDUP
	bool "MCUmgr OTA DFU speedup"
	depends on BT_CTLR || (NCS_SAMPLE_HCI_RPMSG_CHILD_IMAGE || NCS_SAMPLE_MULTIPROTOCOL_RPMSG_CHILD_IMAGE)
	help
 Enable this option to speed up the OTA DFU transfer over Bluetooth.
 This option extends the Bluetooth buffers to extend Bluetooth MTU
 size. The buffer configuration should be the same in the Network Core
 and Application Core image.

 This configuration option is automatically applied for the Network
 Core child image if the NCS_SAMPLE_MCUMGR_BT_OTA_DFU_SPEEDUP option is
 enabled in the main image.

if NCS_SAMPLE_MCUMGR_BT_OTA_DFU_SPEEDUP

config BT_L2CAP_TX_MTU
	default 498 if BT_HCI_HOST

config BT_BUF_ACL_TX_SIZE
	default 251

config BT_BUF_ACL_RX_SIZE
	default 502

config BT_CTLR_DATA_LENGTH_MAX
	default 251 if BT_CTLR

endif 
 For what it's worth, here are the exact BT and bootloader configs I'm using: 
 #=======================================================================================================================
# Bluetooth Configuration
#=======================================================================================================================
CONFIG_BT=y
CONFIG_BT_SMP=n
CONFIG_BT_MAX_CONN=10
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_THROUGHPUT=y
CONFIG_BT_COMPANY_ID=0x073A
CONFIG_BT_ATT_PREPARE_COUNT=2
CONFIG_BT_HCI_TX_STACK_SIZE_WITH_PROMPT=y

CONFIG_BT_BUF_CMD_TX_SIZE=251
# CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE=255

CONFIG_BT_CTLR_PHY_2M=y
CONFIG_BT_CTLR_CONN_RSSI=n
CONFIG_BT_CTLR_PHY_CODED=n
CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL=y

CONFIG_BT_DEVICE_NAME=""
CONFIG_BT_DEVICE_NAME_MAX=6
CONFIG_BT_DEVICE_NAME_DYNAMIC=y

CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS=y
CONFIG_BT_GAP_PERIPHERAL_PREF_PARAMS=y

CONFIG_BT_GATT_CACHING=y
CONFIG_BT_GATT_SERVICE_CHANGED=y
CONFIG_BT_GATT_ENFORCE_SUBSCRIPTION=n

# Make sure supervision timeout is always 5 seconds (500 * 10ms)
CONFIG_BT_PERIPHERAL_PREF_TIMEOUT=500

CONFIG_BT_USER_PHY_UPDATE=y
CONFIG_BT_USER_DATA_LEN_UPDATE=y


#=======================================================================================================================
# Bootloader / Firmware Configuration
#=======================================================================================================================
CONFIG_MCUMGR=y
CONFIG_MCUMGR_TRANSPORT_BT=y
CONFIG_MCUMGR_TRANSPORT_BT_AUTHEN=n
CONFIG_MCUMGR_TRANSPORT_BT_REASSEMBLY=y
CONFIG_MCUMGR_TRANSPORT_BT_CONN_PARAM_CONTROL=y
CONFIG_MCUMGR_TRANSPORT_NETBUF_COUNT=6
CONFIG_MCUMGR_TRANSPORT_WORKQUEUE_STACK_SIZE=4608

CONFIG_MCUMGR_GRP_IMG=y
CONFIG_MCUMGR_GRP_IMG_UPLOAD_CHECK_HOOK=y
CONFIG_MCUMGR_MGMT_NOTIFICATION_HOOKS=y

CONFIG_IMG_MANAGER=y
CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU=y
CONFIG_MCUBOOT_BOOTLOADER_MODE_DIRECT_XIP=y

DFU upload speed through BT SMP is slow

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