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

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Message-ID: <87zkrj4llx.fsf@depni.sinp.msu.ru>
Date:	Sun, 02 Jan 2011 10:59:38 +0000
From:	Serge Belyshev <belyshev@...ni.sinp.msu.ru>
To:	Matthew Wilcox <matthew@....cx>
Cc:	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

Matthew Wilcox <matthew@....cx> writes:

> Disabling NO_HZ has a serious negative effect on performance -- an extra
> 70us per I/O.  Prevent users from deselecting it.

This is rather non-trivial change.

The common wisdom was that NO_HZ=y *adds* overhead, not removes it.
Thus, I propose:

(1) Retaining and elaborating the help text.
(2) Allow user to change the default.
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