1.4.5. fp-cpu-usage

From Linux point of view, the fast path process always appears to consume 100% of the CPUs that are allocated to it. This is because even if the fast path does not receive packets, it continuously polls the NICs for new packets. Therefore, a tool such as top always shows 100% CPU usage.

The fp-cpu-usage tool allows to see the actual load of the fast path CPUs.

Example: an idle fast path using 2 cores:

# fp-cpu-usage
Fast path CPU usage:
cpu: %busy     cycles
 20:   <1%    2043136
 21:   <1%    2034404
average cycles/packets received from NIC: --- (4077540/0)
# top -n 1
(...)
   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 20490 root      20   0  902232 314380 295140 R 207.5  1.0   8:58.49 fp-rte:20
(...)