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SubjectRe: [PATCH] i386: Selectable Frequency of the Timer Interrupt.
On Mon, 16 May 2005, Linus Torvalds wrote:

> or something. You can even maje the Kconfig parts be a separate Kconfig.HZ
> file, and have both the x86 and x86-64 Kconfig files just include the
> common part (since it's a generic issue, not even PC-related: we might
> want to allow things like 60Hz frequencies for CONFIG_EMBEDDED etc, and
> these choices are really valid on any system that allows for the timer to
> be reprogrammed)

Ok. Here is the patch redone. The location for Kconfig.hz is in the
kernel directory since the other timer related stuff is there too:

---
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@lameter.com>
Signed-off-by: Shai Fultheim <shai@scalex86.org>

Index: linux-2.6.12-rc4/arch/i386/Kconfig
===================================================================
--- linux-2.6.12-rc4.orig/arch/i386/Kconfig 2005-05-17 02:19:55.000000000 +0000
+++ linux-2.6.12-rc4/arch/i386/Kconfig 2005-05-17 05:27:31.000000000 +0000
@@ -1133,6 +1133,8 @@
a work-around for a number of buggy BIOSes. Switch this option on if
your computer crashes instead of powering off properly.

+source kernel/Kconfig.hz
+
endmenu

source "arch/i386/kernel/cpu/cpufreq/Kconfig"
Index: linux-2.6.12-rc4/include/asm-i386/param.h
===================================================================
--- linux-2.6.12-rc4.orig/include/asm-i386/param.h 2005-05-17 05:08:56.000000000 +0000
+++ linux-2.6.12-rc4/include/asm-i386/param.h 2005-05-17 05:10:08.000000000 +0000
@@ -1,8 +1,10 @@
+#include <linux/config.h>
+
#ifndef _ASMi386_PARAM_H
#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
Index: linux-2.6.12-rc4/arch/x86_64/Kconfig
===================================================================
--- linux-2.6.12-rc4.orig/arch/x86_64/Kconfig 2005-05-17 02:19:54.000000000 +0000
+++ linux-2.6.12-rc4/arch/x86_64/Kconfig 2005-05-17 05:20:49.000000000 +0000
@@ -410,6 +410,8 @@

If unsure, say Y. Only embedded should say N here.

+source kernel/Kconfig.hz
+
endmenu

#
Index: linux-2.6.12-rc4/include/asm-x86_64/param.h
===================================================================
--- linux-2.6.12-rc4.orig/include/asm-x86_64/param.h 2005-05-17 05:08:52.000000000 +0000
+++ linux-2.6.12-rc4/include/asm-x86_64/param.h 2005-05-17 05:09:42.000000000 +0000
@@ -1,9 +1,11 @@
+#include <linux/config.h>
+
#ifndef _ASMx86_64_PARAM_H
#define _ASMx86_64_PARAM_H

#ifdef __KERNEL__
-# define HZ 1000 /* Internal kernel timer frequency */
-# define USER_HZ 100 /* .. some user interfaces are in "ticks */
+# 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

Index: linux-2.6.12-rc4/kernel/Kconfig.hz
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.12-rc4/kernel/Kconfig.hz 2005-05-17 05:24:01.000000000 +0000
@@ -0,0 +1,46 @@
+#
+# Timer Interrupt Frequency Configuration
+#
+
+choice
+ prompt "Timer frequency"
+ default HZ_250
+ 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.
+
+
+ config HZ_100
+ bool "100 HZ"
+ help
+ 100 HZ is a typical choice for servers, SMP and NUMA systems
+ with lots of processors that may show reduced performance if
+ too many timer interrupts are occurring.
+
+ config HZ_250
+ bool "250 HZ"
+ help
+ 250 HZ is a good compromise choice allowing server performance
+ while also showing good interactive responsiveness even
+ on SMP and NUMA systems.
+
+ config HZ_1000
+ bool "1000 HZ"
+ help
+ 1000 HZ is the preferred choice for desktop systems and other
+ systems requiring fast interactive responses to events.
+
+endchoice
+
+config HZ
+ int
+ default 100 if HZ_100
+ default 250 if HZ_250
+ default 1000 if HZ_1000
+
-
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