linux-kernel - Re: [PATCH] Prevent users from disabling tickless

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Date:	Sun, 02 Jan 2011 10:15:42 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Matthew Wilcox <matthew@....cx>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Prevent users from disabling tickless

Le dimanche 02 janvier 2011 à 09:57 +0100, Pavel Machek a écrit :
> 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@...ux.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?

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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