UDP Packets dropping from host to VM

[mattygio77]

My setup:

Workstation Pro 15.5

Host

CPUs: 16 cores, 32 threads

RAM: 128 GB

OS: Cent OS 7.6.1810

5 NICs - 2x40 Gbps, 2x10Gbps, 1x10Gbps

VM

CPUs: 16 threads

RAM: 64 GB

OS: Red Hat Enterprise 7.8

2 VNICs - 2x10 Gbps

I'm trying to transfer UDP packets from Host to VM using iperf command at 850 Mbps bandwidth. In the attached screen shots. I am dropping about 2-3% of my packets. I have MTU=9000 in all the ifcfg files for all the VNICs and NICs.

What configurations do I need to change to stop packet loss between Host and VM?

[mattygio77]

I've tried increasing the rx ring buffer.

Also, using the vmware-netcfg tool, I set up 2 bridge connections for the virtual NICs to latch on too. Sorry if I'm not using the correct vernacular.

[Matt221177]

Were you able to solve this?  If so, may I ask how?

[mkubecek]

I'm not sure if this is an actual problem. Unlike TCP, UDP has no loss detection/recovery or flow control on its own. So the UDP throughput benchmarks simply make sender throw packets at receiver as fast as possible and if the bottleneck is on receiver side or somewhere in between, there is a loss and the actual throughput should be calculated only from packets which get through. That's how netperf's UDP_STREAM mode works and it's quite likely it's the same for iperf.