pcap_sendqueue_transmit() accuracy

Hello,
I am using the function pcap_sendqueue_transmit() to transmit high rate 64 bytes packets (from 600 packets/s to 60000 packets/s).

Depending on the type of test, packet interval can vary from ~1666us to 16us.

In the setup, I am using a ProfiTap 100M to hardware timestamp the traffic.

For 1666us packet interval, min, max is has follow:

For 16us packet interval, min, max is has follow:

I understand that 16us packet rate is very high but with 1666us, I don't understand why the jitter is so important.

I used different computers (with different adapters) to do this type of test but each time, I see the same behavior.
I mean, jitter can be very important and not constant.

I don't think there is a problem with npcap driver. I only want to know if there is something I can do to reduce this jitter.

Tests are made on Windows 11 Version 23H2 Build 22631.3880

DiagReport for Npcap ( https://npcap.com )

Script Architecture: 64-bit
Script Path: C:\Program Files\Npcap\DiagReport.ps1
Current Time: 08/29/2024 11:15:48
Npcap install path: C:\Program Files\Npcap
Npcap Version: 1.79
PowerShell Version: 5.1.22621.3880

CPU Info:

Name : Intel(R) Xeon(R) W-2125 CPU @ 4.00GHz
Manufacturer : GenuineIntel
DeviceID : CPU0
NumberOfCores : 4
NumberOfEnabledCore : 4
NumberOfLogicalProcessors : 8
Addresswidth : 64

Memory Info:

Size: 32495 MB (34073821184 Bytes)

Best regards,
Cyril

Start by reviewing the pcap_sendqueue_transmit() API and reproducing the reported 1666us and 16us packet-interval tests on Windows 11 with the ProfiTap hardware timestamping setup. Compare results across the listed adapters and Npcap 1.79 diagnostics; done means identifying the source of the jitter or documenting a supported way to reduce it.