6.5.1

Table Of Contents
Solution
n
Increase the threshold in bytes at which Windows changes its behavior for UDP packets by modifying
the registry of the Windows guest OS.
a Locate the HKLM\System\CurrentControlSet\Services\Afd\Parameters registry key.
b Add a value with the name FastSendDatagramThreshold of type DWORD equal to 1500.
For information about fixing this issue in the Windows registry, see
http://support.microsoft.com/kb/235257.
n
Modify the coalescing settings of the virtual machine NIC.
If the Windows virtual machine has a VMXNET3 vNIC adapter, configure one of the following
parameters in the .vmx file of the virtual machine. Use the vSphere Web Client, or directly modify
the .vmx file.
Action Parameter Value
Increase the interrupt rate of the virtual machine to a higher rate than expected
packet rate. For example, if the expected packet rate is 15000 interrupts per
second, set the interrupt rate to 16000 interrupts per second. Set the
ethernetX.coalescingScheme parameter to rbc and the
ethernetX.coalescingParams parameter to 16000. The default interrupt rate
is 4000 interrupts per second.
ethernetX.coalescingScheme
ethernetX.coalescingParams
rbc
16000
Disable coalescing for low throughput or latency-sensitive workloads. For
information about configuring low-latency workloads, see Best Practices for
Performance Tuning of Latency-Sensitive Workloads in vSphere VMs.
ethernetX.coalescingScheme
disabled
Revert to the coalescing algorithm from earlier ESXi releases.
Note The ability to revert to the earlier algorithm will not be available in later
vSphere releases.
ethernetX.coalescingScheme
calibrate
X next to ethernet stands for the sequence number of the vNIC in the virtual machine.
For more information about configuring parameters in the .vmx file, see the vSphere Virtual Machine
Administrationdocumentation.
n
Modify ESXi host coalescing settings.
This approach affects all virtual machines and all virtual machine NICs on the host.
You can edit the advanced system settings list for the host in the vSphere Web Client, or by using a
vCLI console command on the host from the ESXi Shell.
vSphere Troubleshooting
VMware, Inc. 98