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
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