Yes, ~5% is typical usage:
[22.01-RELEASE][admin@7100.stevew.lan]/root: top -aSH
last pid: 66887; load averages: 0.16, 0.16, 0.08 up 0+00:03:03 12:54:54
579 threads: 5 running, 547 sleeping, 27 waiting
CPU: 0.0% user, 0.0% nice, 1.8% system, 0.0% interrupt, 98.2% idle
Mem: 99M Active, 62M Inact, 398M Wired, 7302M Free
ARC: 175M Total, 30M MFU, 142M MRU, 32K Anon, 597K Header, 2248K Other
48M Compressed, 125M Uncompressed, 2.61:1 Ratio
Swap: 1024M Total, 1024M Free
PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND
11 root 155 ki31 0B 64K CPU0 0 2:53 99.77% [idle{idle: cpu0}]
11 root 155 ki31 0B 64K CPU2 2 2:54 99.73% [idle{idle: cpu2}]
11 root 155 ki31 0B 64K CPU3 3 3:00 98.26% [idle{idle: cpu3}]
11 root 155 ki31 0B 64K RUN 1 3:04 93.52% [idle{idle: cpu1}]
8 root -16 - 0B 16K e6000s 1 0:11 6.37% [e6000sw tick kproc]
65687 root 20 0 14M 4668K CPU1 1 0:00 0.16% top -aSH
The process polls the switch IC for the port status once a second. It does so using the MDIO bus via ix2 but that process is slow in the ix driver so it ends up using significant CPU time.
The same process in the 2100 or 3100 is faster via the mvneta driver so it appears to use less CPU time there.
Steve