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>
68 lines
1.9 KiB
C
68 lines
1.9 KiB
C
#ifndef _ASMi386_TIMER_H
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#define _ASMi386_TIMER_H
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#include <linux/init.h>
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/**
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* struct timer_ops - used to define a timer source
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*
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* @name: name of the timer.
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* @init: Probes and initializes the timer. Takes clock= override
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* string as an argument. Returns 0 on success, anything else
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* on failure.
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* @mark_offset: called by the timer interrupt.
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* @get_offset: called by gettimeofday(). Returns the number of microseconds
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* since the last timer interupt.
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* @monotonic_clock: returns the number of nanoseconds since the init of the
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* timer.
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* @delay: delays this many clock cycles.
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*/
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struct timer_opts {
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char* name;
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void (*mark_offset)(void);
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unsigned long (*get_offset)(void);
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unsigned long long (*monotonic_clock)(void);
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void (*delay)(unsigned long);
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unsigned long (*read_timer)(void);
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};
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struct init_timer_opts {
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int (*init)(char *override);
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struct timer_opts *opts;
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};
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#define TICK_SIZE (tick_nsec / 1000)
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extern struct timer_opts* __init select_timer(void);
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extern void clock_fallback(void);
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void setup_pit_timer(void);
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/* Modifiers for buggy PIT handling */
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extern int pit_latch_buggy;
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extern struct timer_opts *cur_timer;
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extern int timer_ack;
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/* list of externed timers */
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extern struct timer_opts timer_none;
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extern struct timer_opts timer_pit;
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extern struct init_timer_opts timer_pit_init;
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extern struct init_timer_opts timer_tsc_init;
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#ifdef CONFIG_X86_CYCLONE_TIMER
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extern struct init_timer_opts timer_cyclone_init;
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#endif
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extern unsigned long calibrate_tsc(void);
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extern unsigned long read_timer_tsc(void);
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extern void init_cpu_khz(void);
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extern int recalibrate_cpu_khz(void);
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#ifdef CONFIG_HPET_TIMER
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extern struct init_timer_opts timer_hpet_init;
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extern unsigned long calibrate_tsc_hpet(unsigned long *tsc_hpet_quotient_ptr);
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#endif
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#ifdef CONFIG_X86_PM_TIMER
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extern struct init_timer_opts timer_pmtmr_init;
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#endif
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#endif
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