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SubjectRe: CONFIG_NO_HZ: missed ticks, stall (keyb IRQ required) [2.6.18-rc4-mm1]

* Andreas Mohr <andi@rhlx01.fht-esslingen.de> wrote:

> The results are (waited for values to settle down each time):
>
> -dyntick4, C1, CONFIG_NO_HZ:
> 83.9W KDE idle, 95.2W bash while 1
> -dyntick4, C2 (C1-only hack disabled, kernel rebuilt), CONFIG_NO_HZ off:
> 84.4W KDE idle, 95.4W bash while 1
> -dyntick4, acpi=off (i.e. APM active), -dynticks:
> 85.5W KDE idle, 95.5W bash while 1
>
> Bet you didn't see this coming...

interesting that there's any savings from dynticks in this workload.
When the CPU is busy then dynticks generates the usual HZ scheduler
tick.

could you try the same measurement with a completely idle system too?
That is where dynticks has its true effects: longer idle intervals. (but
even on an idle system dynticks might not make a difference unless the
hardware can utilize the much larger and more predictable idle times
that dynticks offers.)

Ingo
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