Hi,
I have been measuring UDP roundtrip times with several different Intel Gigabit
Ethernet Controllers (on two Haswell based systems, peer to peer connection).
There seems to be a quite large variation in roundtrip time with newer
controllers getting worse numbers.
I was expecting round trip time in the order of 30 to 40 µs (or better) which
is based on previous results, for example
http://sourceforge.net/p/e1000/mailman/message/19120013/ and
http://tech-forge.com/Latency_SBAC2007.pdf
I am disabling RX interrupt moderation on both peers and getting these
roundtrip times for 1 byte UDP messages:
Intel I210 controller 75
µs
Intel I350 controller 92 µs
Intel 82574L controller 42 µs
The numbers are very consistent, so there is only minimal variation.
The benchmark is run under QNX 6.5.0 (where a single Ethernet driver
"devnp-e1000.so" supports all three cards).
As mentioned the RX interrupt moderation was explicitly disabled by setting the
"int_mod=0" parameter.
A was also able to see that the CPU is only busy (test application, network
stack, kernel) for less than 10µs, so the seems to be some hardware effect
involved.
Are there any known difference regarding the internal RX/TX latency of these
controllers?
Are there any configuration option/register setting besides interrupt
moderation that can explain these differences?
Thanks in advance
Ralf
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