Linux detect my SN750 as SN720 and the read speed CAN NOT reach its claim 3400MB/s

Hi all,
I’ve bought SN750 500GB nvme sdd recently (WDS500G3XHC-00SJG0). When I test this new drive on linux platform, I found its read speed can not reach over 3000MB/s but only 2G.

Due to already format as ext4 partition of whole disk, I can’t do futher test on windows platform but the information which WD SSD Dashboard responsed seems normal.

Is any one can help me find out any exist untuned features that cause this problem ? If yo have same experience, please help me.

------ Environment
Debian Buster 10.1 with kernel 4.19.0-6-amd64
CPU: i5-9400
MB: Asus Rog Strix B360-F Gaming
RAM: Kingston DDR4 2666 16G * 2
Graphic card: MSI GTX1660Ti Ventus

----- supplement information
> blythe@b-pc: ~ $ sudo lspci -vv | grep WD -A 9
> 02:00.0 Non-Volatile memory controller: Sandisk Corp WD Black 2018/PC SN720 NVMe SSD (prog-if 02 [NVM Express])
> Subsystem: Sandisk Corp WD Black 2018/PC SN720 NVMe SSD
> Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
> Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- SERR- Latency: 0, Cache Line Size: 64 bytes
> Interrupt: pin A routed to IRQ 16
> NUMA node: 0
> Region 0: Memory at 91200000 (64-bit, non-prefetchable) [size=16K]
> Region 4: Memory at 91204000 (64-bit, non-prefetchable) [size=256]
> Capabilities: [80] Power Management version 3
> Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
> –
> 04:00.0 Non-Volatile memory controller: Sandisk Corp WD Black 2018/PC SN520 NVMe SSD (rev 01) (prog-if 02 [NVM Express])
> Subsystem: Sandisk Corp WD Black 2018/PC SN520 NVMe SSD
> Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
> Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- SERR- Latency: 0, Cache Line Size: 64 bytes
> Interrupt: pin A routed to IRQ 16
> NUMA node: 0
> Region 0: Memory at 91100000 (64-bit, non-prefetchable) [size=16K]
> Capabilities: [80] Power Management version 3
> Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
> Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-

SN500 (WD blue 256G) plug at m.2 number 1 slot (the one near CPU)
SN750 plug at m.2 number 2 slot ( the one near PCH chip)

Thanks