#44 latency in communication

[Lorenzo Natale]

Ports seem to have latency of up to 40ms when messages are sent with low frequency (>>50ms). Frequent messages (e.g. rate ~50ms) have an initial latency of 40ms, which suddenly drops (0.2-0.3ms) after a few messages are transmitted.

These tests are performed through TCP, locally on the same machine. OS is Linux Debian Stable machine.

Test code:
$YARP_ROOT/example/profiling/port_latency.cpp

[Paul Fitzpatrick]

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This sounds more like a scheduler issue rather than communications per se. This may well be sensitive to kernel version. You might want to try a more recent kernel, there have been improvements in realtime-ish behavior.

[Paul Fitzpatrick]

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Effect is kernel dependent; latencies are low in more recent kernels. Working hypothesis: this is basically a scheduler issue, rather than communications per se. More testing to be done.

[Lorenzo Natale]

More tests proved this to be due to the kernel. Kernels more recent than 2.6.18 don't have such a large latency.