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x86: use cpu_khz for loops_per_jiffy calculation 

On the x86 platform we can use the value of tsc_khz computed during tsc
calibration to calculate the loops_per_jiffy value. Its very important
to keep the error in lpj values to minimum as any error in that may
result in kernel panic in check_timer. In virtualization environment, On
a highly overloaded host the guest delay calibration may sometimes
result in errors beyond the ~50% that timer_irq_works can handle,
resulting in the guest panicking.

Does some formating changes to lpj_setup code to now have a single
printk to print the bogomips value.

We do this only for the boot processor because the AP's can have
different base frequencies or the BIOS might boot a AP at a different
frequency.

Signed-off-by: Alok N Kataria <akataria@vmware.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Daniel Hecht <dhecht@vmware.com>
Cc: Tim Mann <mann@vmware.com>
Cc: Zach Amsden <zach@vmware.com>
Cc: Sahil Rihan <srihan@vmware.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Alok Kataria 2008-06-20 15:06:33 -07:00 committed by Ingo Molnar
parent e01b70ef3e
commit 3da757daf8
4 changed files with 27 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/kernel/time_64.c
View File

@ -123,6 +123,8 @@ void __init time_init(void)
(boot_cpu_data.x86_vendor == X86_VENDOR_AMD))
cpu_khz = calculate_cpu_khz();
lpj_tsc = ((unsigned long)tsc_khz * 1000)/HZ;
if (unsynchronized_tsc())
mark_tsc_unstable("TSCs unsynchronized");

5
arch/x86/kernel/tsc_32.c
View File

@ -401,6 +401,7 @@ static inline void check_geode_tsc_reliable(void) { }
void __init tsc_init(void)
{
int cpu;
u64 lpj;
if (!cpu_has_tsc || tsc_disabled) {
/* Disable the TSC in case of !cpu_has_tsc */
@ -421,6 +422,10 @@ void __init tsc_init(void)
return;
}
lpj = ((u64)tsc_khz * 1000);
do_div(lpj, HZ);
lpj_tsc = lpj;
printk("Detected %lu.%03lu MHz processor.\n",
(unsigned long)cpu_khz / 1000,
(unsigned long)cpu_khz % 1000);

1
include/linux/delay.h
View File

@ -41,6 +41,7 @@ static inline void ndelay(unsigned long x)
#define ndelay(x) ndelay(x)
#endif
extern unsigned long lpj_tsc;
void calibrate_delay(void);
void msleep(unsigned int msecs);
unsigned long msleep_interruptible(unsigned int msecs);

36
init/calibrate.c
View File

@ -8,7 +8,9 @@
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/timex.h>
#include <linux/smp.h>
unsigned long lpj_tsc;
unsigned long preset_lpj;
static int __init lpj_setup(char *str)
{
@ -108,6 +110,10 @@ static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
* This is the number of bits of precision for the loops_per_jiffy. Each
* 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
* the cpu frequency, hence do the calibration for those.
*/
#define LPS_PREC 8
@ -118,20 +124,20 @@ void __cpuinit calibrate_delay(void)
if (preset_lpj) {
loops_per_jiffy = preset_lpj;
printk("Calibrating delay loop (skipped)... "
"%lu.%02lu BogoMIPS preset\n",
loops_per_jiffy/(500000/HZ),
(loops_per_jiffy/(5000/HZ)) % 100);
printk(KERN_INFO
"Calibrating delay loop (skipped) preset value.. ");
} else if ((smp_processor_id() == 0) && lpj_tsc) {
loops_per_jiffy = lpj_tsc;
printk(KERN_INFO
"Calibrating delay loop (skipped), "
"using tsc calculated value.. ");
} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
printk("Calibrating delay using timer specific routine.. ");
printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
loops_per_jiffy/(500000/HZ),
(loops_per_jiffy/(5000/HZ)) % 100,
loops_per_jiffy);
printk(KERN_INFO
"Calibrating delay using timer specific routine.. ");
} else {
loops_per_jiffy = (1<<12);
printk(KERN_DEBUG "Calibrating delay loop... ");
printk(KERN_INFO "Calibrating delay loop... ");
while ((loops_per_jiffy <<= 1) != 0) {
/* wait for "start of" clock tick */
ticks = jiffies;
@ -161,12 +167,8 @@ void __cpuinit calibrate_delay(void)
if (jiffies != ticks) /* longer than 1 tick */
loops_per_jiffy &= ~loopbit;
}
/* Round the value and print it */
printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
loops_per_jiffy/(500000/HZ),
(loops_per_jiffy/(5000/HZ)) % 100,
loops_per_jiffy);
}
printk(KERN_INFO "%lu.%02lu BogoMIPS (lpj=%lu)\n",
loops_per_jiffy/(500000/HZ),
(loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
}