Re: [PATCH] Prevent users from disabling tickless

From: Eric Dumazet
Date: Sun Jan 02 2011 - 04:16:03 EST

Le dimanche 02 janvier 2011 Ã 09:57 +0100, Pavel Machek a Ãcrit :
> 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@xxxxxxxxxxxxxxx>
> 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?

Also, where are those 70us spent exactly ? Once per clock tick ?

For me, I/O can be an ethernet frame sent or received, and I never
noticed such a delay.

At least, commit message sounds very evasive too me.

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