8a9e1b0f56
Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
35 lines
631 B
C
35 lines
631 B
C
/*
|
|
* linux/include/asm-x86_64/timex.h
|
|
*
|
|
* x86-64 architecture timex specifications
|
|
*/
|
|
#ifndef _ASMx8664_TIMEX_H
|
|
#define _ASMx8664_TIMEX_H
|
|
|
|
#include <linux/config.h>
|
|
#include <asm/8253pit.h>
|
|
#include <asm/msr.h>
|
|
#include <asm/vsyscall.h>
|
|
#include <asm/hpet.h>
|
|
|
|
#define CLOCK_TICK_RATE PIT_TICK_RATE /* Underlying HZ */
|
|
|
|
typedef unsigned long long cycles_t;
|
|
|
|
static inline cycles_t get_cycles (void)
|
|
{
|
|
unsigned long long ret;
|
|
|
|
rdtscll(ret);
|
|
return ret;
|
|
}
|
|
|
|
extern unsigned int cpu_khz;
|
|
|
|
extern int read_current_timer(unsigned long *timer_value);
|
|
#define ARCH_HAS_READ_CURRENT_TIMER 1
|
|
|
|
extern struct vxtime_data vxtime;
|
|
|
|
#endif
|