Commit 3da757da authored by Alok Kataria's avatar Alok Kataria Committed by Ingo Molnar
Browse files

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: default avatarAlok 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: default avatarIngo Molnar <mingo@elte.hu>
parent e01b70ef

arch/x86/kernel/time_64.c

+2 −0
Original line number Diff line number Diff line
@@ -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");

arch/x86/kernel/tsc_32.c

+5 −0
Original line number Diff line number Diff line
@@ -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);

include/linux/delay.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

init/calibrate.c

+19 −17
Original line number Diff line number Diff line
@@ -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);

}

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