On APM82181, "vmstat" (/proc/stat) doesn't show correct idle percent, if
kernel enables "CONFIG_NO_HZ" (Tickless System / Dynamic Tick).
When I run wireless throughput test with heavy traffic, "vmstat" shows very
high idle percent while "oprofile" shows very low idle percent. During the
test, the system is idle, but network traffic uses a lot of hard IRQ and
soft-irq time. "vmstat" would have the correct stats if
account_idle_ticks(ticks) in kernel/time/tick-sched.c doesn't add more idle
time in "vmstat". In the same test, if I disable "CONFIG_NO_HZ" in kernel,
idle percent in "vmstat" and "oprofile" would match.
My APM82181 kernel configuration is "CONFIG_NO_HZ", "CONFIG_HZ_250=y",
"CONFIG_HZ=250", and "CONFIG_HIGH_RES_TIMERS".
My question is that if kernel enables "CONFIG_NO_HZ", how would kernel
report correct stats.
Thanks,
Fushen