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

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Date:	Tue, 21 Dec 2010 16:39:43 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] Prevent users from disabling tickless


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>

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"

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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