Onload uses the Time Stamp Counter (TSC) CPU registers to measure changes in time with very low overhead. Modern CPUs support an “invariant TSC”, which is synchronized across different CPUs and ticks at a constant rate regardless of the current CPU frequency and power saving mode. Onload relies on this to generate accurate time calculations when running across multiple CPUs. If run on a system which does not have an invariant TSC, Onload might calculate wildly inaccurate time values and this can, in extreme cases, lead to some connections becoming stuck.
Users should consult their server vendor documentation and OS documentation to ensure that servers can meet the invariant TSC requirement.