Linus Torvalds wrote:
On Thu, 14 Jul 2005, Lee Revell wrote:
I don't think this will fly because we take a big performance hit by
calculating HZ at runtime.
I think it might be an acceptable solution for a distribution that really
needed it, since it should be fairly simple. However, it's definitely not
the right solution.
HOWEVER. I bet that somebody who really really cares (hint hint) could
easily make HZ be 1000, and then dynamically tweak the divisor at bootup
to be either 1000, 250, or 100, and then increment "jiffies" by 1, 4 or
10.
My wild guess is that this is 20 lines of code, plus another 20 for
"setup", so that you can choose between 100/250/1000 Hz with a kernel
command line.
It wouldn't be "dynamic" at first - you'd just set it up at bootup, and
set a "jiffies_increment" variable, and change the
jiffies_64++;
into
jiffies_64 += jiffies_increment;
and you'd be done.
Really. I dare you guys. First one to send me a tested patch gets a gold
star.
I don't know if this will earn me that gold star or not, but it's what I
have at this point.
It's buggy, that I know. setting kernel_hz (the new boot parameter) to
250 causes my system clock to run at something like 4-5 times normal
speed, and key repeat is all funny (super fast) and various other nasty
things - however, it does build and it does boot (i386 only as that's
all I have) and apart from the kernels notion of time being way off it
does seem to be a step in the right direction.
Me never having looked at the kernels timer code before is most likely
the explanation for the bugs - that and the fact that I didn't try to
tackle the bogomips calculation at all... Ohh, and it'll probably bee
even more strange if you build the kernel with CONFIG_HZ set to anything
other than 1000 - if this is what we want to do, then I guess CONFIG_HZ
needs to go away completely and just always be 1000 and then people
should use the boot option to modify if needed/wanted.
Anyway, is this somewhere along the lines of what you were thinking?
The patch is below, but I've also attached it since I suspect
thunderbird will mangle it.
diff -upr linux-2.6.13-rc3-orig/arch/i386/kernel/time.c
linux-2.6.13-rc3/arch/i386/kernel/time.c
--- linux-2.6.13-rc3-orig/arch/i386/kernel/time.c 2005-07-14
20:33:35.000000000 +0200
+++ linux-2.6.13-rc3/arch/i386/kernel/time.c 2005-07-15
04:02:50.000000000 +0200
@@ -75,6 +75,7 @@ int pit_latch_buggy; /* ext
#include "do_timer.h"
u64 jiffies_64 = INITIAL_JIFFIES;
+u16 jiffies_increment = 1;
EXPORT_SYMBOL(jiffies_64);
@@ -481,3 +482,27 @@ void __init time_init(void)
time_init_hook();
}
+
+static int __init jiffies_increment_setup(char *str)
+{
+ printk(KERN_NOTICE "setting up jiffies_increment : ");
+ if (str) {
+ printk("kernel_hz = %s, ", str);
+ } else {
+ printk("kernel_hz is unset, ");
+ }
+ if (!strncmp("100", str, 3)) {
+ jiffies_increment = 10;
+ printk("jiffies_increment set to 10, effective HZ will be
100\n");
+ } else if (!strncmp("250", str, 3)) {
+ jiffies_increment = 4;
+ printk("jiffies_increment set to 4, effective HZ will be
250\n");
+ } else {
+ jiffies_increment = 1;
+ printk("jiffies_increment set to 1, effective HZ will be
1000\n");
+ }
+
+ return 1;
+}
+
+__setup("kernel_hz=", jiffies_increment_setup);
diff -upr linux-2.6.13-rc3-orig/arch/i386/kernel/timers/timer_pm.c
linux-2.6.13-rc3/arch/i386/kernel/timers/timer_pm.c
--- linux-2.6.13-rc3-orig/arch/i386/kernel/timers/timer_pm.c 2005-07-14
20:33:35.000000000 +0200
+++ linux-2.6.13-rc3/arch/i386/kernel/timers/timer_pm.c 2005-07-15
02:59:39.000000000 +0200
@@ -176,7 +176,7 @@ static void mark_offset_pmtmr(void)
/* compensate for lost ticks */
if (lost >= 2)
- jiffies_64 += lost - 1;
+ jiffies_64 += (lost * jiffies_increment) - 1;
/* don't calculate delay for first run,
or if we've got less then a tick */
diff -upr linux-2.6.13-rc3-orig/arch/i386/kernel/timers/timer_tsc.c
linux-2.6.13-rc3/arch/i386/kernel/timers/timer_tsc.c
--- linux-2.6.13-rc3-orig/arch/i386/kernel/timers/timer_tsc.c 2005-07-14
20:33:35.000000000 +0200
+++ linux-2.6.13-rc3/arch/i386/kernel/timers/timer_tsc.c 2005-07-15
02:59:13.000000000 +0200
@@ -193,7 +193,7 @@ static void mark_offset_tsc_hpet(void)
offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))) {
int lost_ticks = (offset - hpet_last) / hpet_tick;
- jiffies_64 += lost_ticks;
+ jiffies_64 += lost_ticks * jiffies_increment;
}
hpet_last = hpet_current;
@@ -415,7 +415,7 @@ static void mark_offset_tsc(void)
lost = delta/(1000000/HZ);
delay = delta%(1000000/HZ);
if (lost >= 2) {
- jiffies_64 += lost-1;
+ jiffies_64 += (lost * jiffies_increment) - 1;
/* sanity check to ensure we're not always losing ticks */
if (lost_count++ > 100) {
@@ -448,7 +448,7 @@ static void mark_offset_tsc(void)
* usec delta is > 90% # of usecs/tick)
*/
if (lost && abs(delay - delay_at_last_interrupt) > (900000/HZ))
- jiffies_64++;
+ jiffies_64 += jiffies_increment;
}
static int __init init_tsc(char* override)
diff -upr linux-2.6.13-rc3-orig/include/linux/jiffies.h
linux-2.6.13-rc3/include/linux/jiffies.h
--- linux-2.6.13-rc3-orig/include/linux/jiffies.h 2005-06-17
21:48:29.000000000 +0200
+++ linux-2.6.13-rc3/include/linux/jiffies.h 2005-07-15
03:42:57.000000000 +0200
@@ -83,6 +83,7 @@
*/
extern u64 __jiffy_data jiffies_64;
extern unsigned long volatile __jiffy_data jiffies;
+extern u16 jiffies_increment;
#if (BITS_PER_LONG < 64)
u64 get_jiffies_64(void);
diff -upr linux-2.6.13-rc3-orig/kernel/timer.c
linux-2.6.13-rc3/kernel/timer.c
--- linux-2.6.13-rc3-orig/kernel/timer.c 2005-07-14 20:34:24.000000000
+0200
+++ linux-2.6.13-rc3/kernel/timer.c 2005-07-15 02:55:45.000000000 +0200
@@ -948,7 +948,7 @@ static inline void update_times(void)
void do_timer(struct pt_regs *regs)
{
- jiffies_64++;
+ jiffies_64 += jiffies_increment;
update_times();
}
--
Jesper Juhl
diff -upr linux-2.6.13-rc3-orig/arch/i386/kernel/time.c linux-2.6.13-rc3/arch/i386/kernel/time.c
--- linux-2.6.13-rc3-orig/arch/i386/kernel/time.c 2005-07-14 20:33:35.000000000 +0200
+++ linux-2.6.13-rc3/arch/i386/kernel/time.c 2005-07-15 04:02:50.000000000 +0200
@@ -75,6 +75,7 @@ int pit_latch_buggy; /* ext
#include "do_timer.h"
u64 jiffies_64 = INITIAL_JIFFIES;
+u16 jiffies_increment = 1;
EXPORT_SYMBOL(jiffies_64);
@@ -481,3 +482,27 @@ void __init time_init(void)
time_init_hook();
}
+
+static int __init jiffies_increment_setup(char *str)
+{
+ printk(KERN_NOTICE "setting up jiffies_increment : ");
+ if (str) {
+ printk("kernel_hz = %s, ", str);
+ } else {
+ printk("kernel_hz is unset, ");
+ }
+ if (!strncmp("100", str, 3)) {
+ jiffies_increment = 10;
+ printk("jiffies_increment set to 10, effective HZ will be 100\n");
+ } else if (!strncmp("250", str, 3)) {
+ jiffies_increment = 4;
+ printk("jiffies_increment set to 4, effective HZ will be 250\n");
+ } else {
+ jiffies_increment = 1;
+ printk("jiffies_increment set to 1, effective HZ will be 1000\n");
+ }
+
+ return 1;
+}
+
+__setup("kernel_hz=", jiffies_increment_setup);
diff -upr linux-2.6.13-rc3-orig/arch/i386/kernel/timers/timer_pm.c linux-2.6.13-rc3/arch/i386/kernel/timers/timer_pm.c
--- linux-2.6.13-rc3-orig/arch/i386/kernel/timers/timer_pm.c 2005-07-14 20:33:35.000000000 +0200
+++ linux-2.6.13-rc3/arch/i386/kernel/timers/timer_pm.c 2005-07-15 02:59:39.000000000 +0200
@@ -176,7 +176,7 @@ static void mark_offset_pmtmr(void)
/* compensate for lost ticks */
if (lost >= 2)
- jiffies_64 += lost - 1;
+ jiffies_64 += (lost * jiffies_increment) - 1;
/* don't calculate delay for first run,
or if we've got less then a tick */
diff -upr linux-2.6.13-rc3-orig/arch/i386/kernel/timers/timer_tsc.c linux-2.6.13-rc3/arch/i386/kernel/timers/timer_tsc.c
--- linux-2.6.13-rc3-orig/arch/i386/kernel/timers/timer_tsc.c 2005-07-14 20:33:35.000000000 +0200
+++ linux-2.6.13-rc3/arch/i386/kernel/timers/timer_tsc.c 2005-07-15 02:59:13.000000000 +0200
@@ -193,7 +193,7 @@ static void mark_offset_tsc_hpet(void)
offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))) {
int lost_ticks = (offset - hpet_last) / hpet_tick;
- jiffies_64 += lost_ticks;
+ jiffies_64 += lost_ticks * jiffies_increment;
}
hpet_last = hpet_current;
@@ -415,7 +415,7 @@ static void mark_offset_tsc(void)
lost = delta/(1000000/HZ);
delay = delta%(1000000/HZ);
if (lost >= 2) {
- jiffies_64 += lost-1;
+ jiffies_64 += (lost * jiffies_increment) - 1;
/* sanity check to ensure we're not always losing ticks */
if (lost_count++ > 100) {
@@ -448,7 +448,7 @@ static void mark_offset_tsc(void)
* usec delta is > 90% # of usecs/tick)
*/
if (lost && abs(delay - delay_at_last_interrupt) > (900000/HZ))
- jiffies_64++;
+ jiffies_64 += jiffies_increment;
}
static int __init init_tsc(char* override)
diff -upr linux-2.6.13-rc3-orig/include/linux/jiffies.h linux-2.6.13-rc3/include/linux/jiffies.h
--- linux-2.6.13-rc3-orig/include/linux/jiffies.h 2005-06-17 21:48:29.000000000 +0200
+++ linux-2.6.13-rc3/include/linux/jiffies.h 2005-07-15 03:42:57.000000000 +0200
@@ -83,6 +83,7 @@
*/
extern u64 __jiffy_data jiffies_64;
extern unsigned long volatile __jiffy_data jiffies;
+extern u16 jiffies_increment;
#if (BITS_PER_LONG < 64)
u64 get_jiffies_64(void);
diff -upr linux-2.6.13-rc3-orig/kernel/timer.c linux-2.6.13-rc3/kernel/timer.c
--- linux-2.6.13-rc3-orig/kernel/timer.c 2005-07-14 20:34:24.000000000 +0200
+++ linux-2.6.13-rc3/kernel/timer.c 2005-07-15 02:55:45.000000000 +0200
@@ -948,7 +948,7 @@ static inline void update_times(void)
void do_timer(struct pt_regs *regs)
{
- jiffies_64++;
+ jiffies_64 += jiffies_increment;
update_times();
}
