Re: [RFC PATCH] x86:Use cpu_khz for loops_per_jiffy calculation

Alok Kataria
2008-06-24T01:22:06Z

On Mon, 2008-06-23 at 16:47 -0700, Ingo Molnar wrote:
> * Alok Kataria <akataria@vmware.com> wrote:
>
> > IMO, lpj_tsc explains how is this variable initialized. But thinking
> > about it, maybe we should rename it to "lpj_timer" ?
>
> ok. But instead of 'lpj_timer' i'd suggest to use something like
> 'lpj_fine' - as this really is about finegrained measurements.

Ok.
>
> I'd suggest a delta patch against tip/master that renames all those
> tsc_* variables to fine_*. So tsc_rate_min would become fine_rate_min,
> etc.

Ingo, tsc_rate_min etc are related to the timer rate so calling it
fine_rate_min would be confusing IMO. Instead i call it as
timer_rate_min.
Below is the patch on tip/master.
Tested on both 32 and 64 bit environment, tree works fine for me.

--
As suggested by Ingo, remove all references to tsc from init/calibrate.c

TSC is x86 specific, and using tsc in variable names in a generic file should
be avoided. lpj_tsc is now called lpj_fine, since it is related to fine tuning
of lpj value. Also tsc_rate_* is called timer_rate_*

Signed-off-by: Alok N Kataria <akataria@vmware.com>

Index: linux-x86-tree.git/arch/x86/kernel/time_64.c
===================================================================
--- linux-x86-tree.git.orig/arch/x86/kernel/time_64.c 2008-06-23 17:24:07.000000000 -0700
+++ linux-x86-tree.git/arch/x86/kernel/time_64.c 2008-06-23 17:50:51.000000000 -0700
@@ -123,7 +123,7 @@
(boot_cpu_data.x86_vendor == X86_VENDOR_AMD))
cpu_khz = calculate_cpu_khz();

- lpj_tsc = ((unsigned long)tsc_khz * 1000)/HZ;
+ lpj_fine = ((unsigned long)tsc_khz * 1000)/HZ;

if (unsynchronized_tsc())
mark_tsc_unstable("TSCs unsynchronized");
Index: linux-x86-tree.git/arch/x86/kernel/tsc_32.c
===================================================================
--- linux-x86-tree.git.orig/arch/x86/kernel/tsc_32.c 2008-06-23 17:24:07.000000000 -0700
+++ linux-x86-tree.git/arch/x86/kernel/tsc_32.c 2008-06-23 17:50:58.000000000 -0700
@@ -419,7 +419,7 @@

lpj = ((u64)tsc_khz * 1000);
do_div(lpj, HZ);
- lpj_tsc = lpj;
+ lpj_fine = lpj;

/* now allow native_sched_clock() to use rdtsc */
tsc_disabled = 0;
Index: linux-x86-tree.git/include/linux/delay.h
===================================================================
--- linux-x86-tree.git.orig/include/linux/delay.h 2008-06-23 17:24:26.000000000 -0700
+++ linux-x86-tree.git/include/linux/delay.h 2008-06-23 17:51:08.000000000 -0700
@@ -41,7 +41,7 @@
#define ndelay(x) ndelay(x)
#endif

-extern unsigned long lpj_tsc;
+extern unsigned long lpj_fine;
void calibrate_delay(void);
void msleep(unsigned int msecs);
unsigned long msleep_interruptible(unsigned int msecs);
Index: linux-x86-tree.git/init/calibrate.c
===================================================================
--- linux-x86-tree.git.orig/init/calibrate.c 2008-06-23 17:24:26.000000000 -0700
+++ linux-x86-tree.git/init/calibrate.c 2008-06-23 18:05:38.000000000 -0700
@@ -10,7 +10,7 @@
#include <linux/timex.h>
#include <linux/smp.h>

-unsigned long lpj_tsc;
+unsigned long lpj_fine;
unsigned long preset_lpj;
static int __init lpj_setup(char *str)
{
@@ -35,9 +35,9 @@
unsigned long pre_start, start, post_start;
unsigned long pre_end, end, post_end;
unsigned long start_jiffies;
- unsigned long tsc_rate_min, tsc_rate_max;
- unsigned long good_tsc_sum = 0;
- unsigned long good_tsc_count = 0;
+ unsigned long timer_rate_min, timer_rate_max;
+ unsigned long good_timer_sum = 0;
+ unsigned long good_timer_count = 0;
int i;

if (read_current_timer(&pre_start) < 0 )
@@ -81,22 +81,24 @@
}
read_current_timer(&post_end);

- tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
- tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;
+ timer_rate_max = (post_end - pre_start) /
+ DELAY_CALIBRATION_TICKS;
+ timer_rate_min = (pre_end - post_start) /
+ DELAY_CALIBRATION_TICKS;

/*
- * If the upper limit and lower limit of the tsc_rate is
+ * If the upper limit and lower limit of the timer_rate is
* >= 12.5% apart, redo calibration.
*/
if (pre_start != 0 && pre_end != 0 &&
- (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
- good_tsc_count++;
- good_tsc_sum += tsc_rate_max;
+ (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
+ good_timer_count++;
+ good_timer_sum += timer_rate_max;
}
}

- if (good_tsc_count)
- return (good_tsc_sum/good_tsc_count);
+ if (good_timer_count)
+ return (good_timer_sum/good_timer_count);

printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
"estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
@@ -111,8 +113,8 @@
* bit takes on average 1.5/HZ seconds. This (like the original) is a little
* better than 1%
* For the boot cpu we can skip the delay calibration and assign it a value
- * calculated based on the tsc frequency.
- * For the rest of the CPUs we cannot assume that the tsc frequency is same as
+ * calculated based on the timer frequency.
+ * For the rest of the CPUs we cannot assume that the timer frequency is same as
* the cpu frequency, hence do the calibration for those.
*/
#define LPS_PREC 8
@@ -126,11 +128,11 @@
loops_per_jiffy = preset_lpj;
printk(KERN_INFO
"Calibrating delay loop (skipped) preset value.. ");
- } else if ((smp_processor_id() == 0) && lpj_tsc) {
- loops_per_jiffy = lpj_tsc;
+ } else if ((smp_processor_id() == 0) && lpj_fine) {
+ loops_per_jiffy = lpj_fine;
printk(KERN_INFO
"Calibrating delay loop (skipped), "
- "using tsc calculated value.. ");
+ "value calculated using timer frequency.. ");
} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
printk(KERN_INFO
"Calibrating delay using timer specific routine.. ");