[PATCH] i386: Selectable Frequency of the Timer Interrupt.

[christoph <christoph@scalex86.org>]

Make the timer frequency selectable. The timer interrupt may cause bus
and memory contention in large NUMA systems since the interrupt occurs
on each processor HZ times per second.

Signed-off-by: Christoph Lameter <christoph@scale86.org>
Signed-off-by: Shai Fultheim <shai@scalex86.org>

Index: linux-2.6.11/arch/i386/Kconfig
===================================================================
--- linux-2.6.11.orig/arch/i386/Kconfig	2005-05-16 12:07:31.000000000 -0700
+++ linux-2.6.11/arch/i386/Kconfig	2005-05-16 12:39:48.000000000 -0700
@@ -939,6 +939,20 @@ config SECCOMP
 
 	  If unsure, say Y. Only embedded should say N here.
 
+config HZ
+	int "Frequency of the Timer Interrupt (1000 or 100)"
+	range 100 1000
+	default 1000
+	help
+	  Allows the configuration of the timer frequency. It is customary
+	  to have the timer interrupt run at 1000 HZ but 100 HZ may be more
+	  beneficial for servers and NUMA systems that do not need to have
+	  a fast response for user interaction and that may experience bus
+	  contention and cacheline bounces as a result of timer interrupts.
+	  Note that the timer interrupt occurs on each processor in an SMP
+	  environment leading to NR_CPUS * HZ number of timer interrupts
+	  per second.
+
 endmenu
 
 
Index: linux-2.6.11/include/asm-i386/param.h
===================================================================
--- linux-2.6.11.orig/include/asm-i386/param.h	2005-05-16 12:07:25.000000000 -0700
+++ linux-2.6.11/include/asm-i386/param.h	2005-05-16 12:09:04.000000000 -0700
@@ -2,7 +2,7 @@
 #define _ASMi386_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ		1000		/* Internal kernel timer frequency */
+# define HZ		CONFIG_HZ	/* Internal kernel timer frequency */
 # define USER_HZ	100		/* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC		(USER_HZ)	/* like times() */
 #endif
-
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