Often, it is useful to preserve the preset loops_per_jiffy
value for a machine in a config option. Right now, you can
specify a preset lpj value on the kernel command line. But this
means the value is preserved in the firmware, which is less
portable between developers.
This patch provides a config option for preset lpj, which means
the value can be easily preserved, and conveyed between developers
in a config file.
Signed-off-by: Tim Bird <[EMAIL PROTECTED]>
----
diff -pruN linux-2.6.20-rc5-git2.orig/init/Kconfig
linux-2.6.20-rc5-git2/init/Kconfig
--- linux-2.6.20-rc5-git2.orig/init/Kconfig 2007-01-12 10:54:26.000000000
-0800
+++ linux-2.6.20-rc5-git2/init/Kconfig 2007-01-24 16:03:30.000000000 -0800
@@ -466,6 +466,35 @@ config VM_EVENT_COUNTERS
on EMBEDDED systems. /proc/vmstat will only show page counts
if VM event counters are disabled.
+config PRESET_LPJ
+ int "Preset loops_per_jiffy" if EMBEDDED
+ default 0
+ help
+ Set this to preset the number of loops used by delay() to
+ achieve a single jiffy of delay inside the kernel. This is
+ normally calculated at boot time, but that calibration can
+ take up to 250 ms per CPU. Specifying a constant value here
+ eliminates the calibration, and improves bootup time.
+
+ A value of 0 results in the normal autodetect behavior.
+
+ To determine the correct value for your kernel, first set this
+ option to 0, compile and boot the kernel on your target hardware,
+ then see what value is printed during the kernel boot. Use that
+ value here.
+
+ The kernel command line parameter "lpj=" can be used to override
+ the value configured here.
+
+ Note that on SMP systems the preset will be applied to all CPUs,
+ which could cause problems if for some reason your CPUs need
+ significantly divergent settings.
+
+ If unsure, set this to 0. An incorrect value will cause delays in
+ the kernel to be wrong, leading to unpredictable I/O errors and
+ other breakage. Although unlikely, in the extreme case this might
+ damage your hardware.
+
endmenu # General setup
config RT_MUTEXES
diff -pruN linux-2.6.20-rc5-git2.orig/init/calibrate.c
linux-2.6.20-rc5-git2/init/calibrate.c
--- linux-2.6.20-rc5-git2.orig/init/calibrate.c 2007-01-12 10:54:26.000000000
-0800
+++ linux-2.6.20-rc5-git2/init/calibrate.c 2007-01-23 11:23:39.000000000
-0800
@@ -10,7 +10,7 @@
#include <asm/timex.h>
-static unsigned long preset_lpj;
+static unsigned long preset_lpj = CONFIG_PRESET_LPJ;
static int __init lpj_setup(char *str)
{
preset_lpj = simple_strtoul(str,NULL,0);
-
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