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DateSun, 2 Jan 2011 09:57:55 +0100
FromPavel Machek <>
SubjectRe: [PATCH] Prevent users from disabling tickless
Hi!

> Disabling NO_HZ has a serious negative effect on performance -- an extra
> 70us per I/O. Prevent users from deselecting it.
>
> Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

System with fixed HZ is really simpler etc... and 70us per i/o does
not sound that bad.

Anyway, should not i/o overhead just be fixed?
Pavel

> diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
> index f06a8a3..55b9a04 100644
> --- a/kernel/time/Kconfig
> +++ b/kernel/time/Kconfig
> @@ -5,13 +5,9 @@ config TICK_ONESHOT
> bool
>
> config NO_HZ
> - bool "Tickless System (Dynamic Ticks)"
> + def_bool y
> depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
> select TICK_ONESHOT
> - help
> - This option enables a tickless system: timer interrupts will
> - only trigger on an as-needed basis both when the system is
> - busy and when the system is idle.
>
> config HIGH_RES_TIMERS
> bool "High Resolution Timer Support"
>

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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