minix/kernel/arch/i386/arch_clock.c
Tomas Hruby 6aa26565e6 SMP - Big kernel lock (BKL)
- to isolate execution inside kernel we use a big kernel lock
  implemented as a spinlock

- the lock is acquired asap after entering kernel mode and released as
  late as possible. Only one CPU as a time can execute the core kernel
  code

- measurement son real hw show that the overhead of this lock is close
  to 0% of kernel time for the currnet system

- the overhead of this lock may be as high as 45% of kernel time in
  virtual machines depending on the ratio between physical CPUs
  available and emulated CPUs. The performance degradation is
  significant
2010-09-15 14:10:03 +00:00

232 lines
5.5 KiB
C

/* i386-specific clock functions. */
#include <machine/ports.h>
#include <minix/portio.h>
#include "kernel/kernel.h"
#include "kernel/clock.h"
#include "kernel/proc.h"
#include <minix/u64.h>
#include "glo.h"
#ifdef CONFIG_APIC
#include "apic.h"
#endif
#include "spinlock.h"
#define CLOCK_ACK_BIT 0x80 /* PS/2 clock interrupt acknowledge bit */
/* Clock parameters. */
#define COUNTER_FREQ (2*TIMER_FREQ) /* counter frequency using square wave */
#define LATCH_COUNT 0x00 /* cc00xxxx, c = channel, x = any */
#define SQUARE_WAVE 0x36 /* ccaammmb, a = access, m = mode, b = BCD */
/* 11x11, 11 = LSB then MSB, x11 = sq wave */
#define TIMER_FREQ 1193182 /* clock frequency for timer in PC and AT */
#define TIMER_COUNT(freq) (TIMER_FREQ/(freq)) /* initial value for counter*/
/* FIXME make it cpu local! */
PRIVATE u64_t tsc_ctr_switch; /* when did we switched time accounting */
PRIVATE irq_hook_t pic_timer_hook; /* interrupt handler hook */
PRIVATE unsigned probe_ticks;
PRIVATE u64_t tsc0, tsc1;
#define PROBE_TICKS (system_hz / 10)
PRIVATE unsigned tsc_per_ms[CONFIG_MAX_CPUS];
/*===========================================================================*
* init_8235A_timer *
*===========================================================================*/
PUBLIC int init_8253A_timer(const unsigned freq)
{
/* Initialize channel 0 of the 8253A timer to, e.g., 60 Hz,
* and register the CLOCK task's interrupt handler to be run
* on every clock tick.
*/
outb(TIMER_MODE, SQUARE_WAVE); /* run continuously */
outb(TIMER0, (TIMER_COUNT(freq) & 0xff)); /* timer low byte */
outb(TIMER0, TIMER_COUNT(freq) >> 8); /* timer high byte */
return OK;
}
/*===========================================================================*
* stop_8235A_timer *
*===========================================================================*/
PUBLIC void stop_8253A_timer(void)
{
/* Reset the clock to the BIOS rate. (For rebooting.) */
outb(TIMER_MODE, 0x36);
outb(TIMER0, 0);
outb(TIMER0, 0);
}
PRIVATE int calib_cpu_handler(irq_hook_t * UNUSED(hook))
{
u64_t tsc;
probe_ticks++;
read_tsc_64(&tsc);
if (probe_ticks == 1) {
tsc0 = tsc;
}
else if (probe_ticks == PROBE_TICKS) {
tsc1 = tsc;
}
/* just in case we are in an SMP single cpu fallback mode */
BKL_UNLOCK();
return 1;
}
PRIVATE void estimate_cpu_freq(void)
{
u64_t tsc_delta;
u64_t cpu_freq;
irq_hook_t calib_cpu;
/* set the probe, we use the legacy timer, IRQ 0 */
put_irq_handler(&calib_cpu, CLOCK_IRQ, calib_cpu_handler);
/* just in case we are in an SMP single cpu fallback mode */
BKL_UNLOCK();
/* set the PIC timer to get some time */
intr_enable();
/* loop for some time to get a sample */
while(probe_ticks < PROBE_TICKS) {
intr_enable();
}
intr_disable();
/* just in case we are in an SMP single cpu fallback mode */
BKL_LOCK();
/* remove the probe */
rm_irq_handler(&calib_cpu);
tsc_delta = sub64(tsc1, tsc0);
cpu_freq = mul64(div64u64(tsc_delta, PROBE_TICKS - 1), make64(system_hz, 0));
cpu_set_freq(cpuid, cpu_freq);
BOOT_VERBOSE(cpu_print_freq(cpuid));
}
PUBLIC int arch_init_local_timer(unsigned freq)
{
#ifdef CONFIG_APIC
/* if we know the address, lapic is enabled and we should use it */
if (lapic_addr) {
unsigned cpu = cpuid;
lapic_set_timer_periodic(freq);
tsc_per_ms[cpu] = div64u(cpu_get_freq(cpu), 1000);
} else
{
BOOT_VERBOSE(printf("Initiating legacy i8253 timer\n"));
#else
{
#endif
init_8253A_timer(freq);
estimate_cpu_freq();
/* always only 1 cpu in the system */
tsc_per_ms[0] = div64u(cpu_get_freq(0), 1000);
}
return 0;
}
PUBLIC void arch_stop_local_timer(void)
{
#ifdef CONFIG_APIC
if (lapic_addr) {
lapic_stop_timer();
} else
#endif
{
stop_8253A_timer();
}
}
PUBLIC int arch_register_local_timer_handler(const irq_handler_t handler)
{
#ifdef CONFIG_APIC
if (lapic_addr) {
/* Using APIC, it is configured in apic_idt_init() */
BOOT_VERBOSE(printf("Using LAPIC timer as tick source\n"));
} else
#endif
{
/* Using PIC, Initialize the CLOCK's interrupt hook. */
pic_timer_hook.proc_nr_e = NONE;
pic_timer_hook.irq = CLOCK_IRQ;
put_irq_handler(&pic_timer_hook, CLOCK_IRQ, handler);
}
return 0;
}
PUBLIC void cycles_accounting_init(void)
{
read_tsc_64(&tsc_ctr_switch);
}
PUBLIC void context_stop(struct proc * p)
{
u64_t tsc, tsc_delta;
read_tsc_64(&tsc);
tsc_delta = sub64(tsc, tsc_ctr_switch);
p->p_cycles = add64(p->p_cycles, tsc_delta);
tsc_ctr_switch = tsc;
/*
* deduct the just consumed cpu cycles from the cpu time left for this
* process during its current quantum. Skip IDLE and other pseudo kernel
* tasks
*/
if (p->p_endpoint >= 0) {
#if DEBUG_RACE
make_zero64(p->p_cpu_time_left);
#else
/* if (tsc_delta < p->p_cpu_time_left) in 64bit */
if (tsc_delta.hi < p->p_cpu_time_left.hi ||
(tsc_delta.hi == p->p_cpu_time_left.hi &&
tsc_delta.lo < p->p_cpu_time_left.lo))
p->p_cpu_time_left = sub64(p->p_cpu_time_left, tsc_delta);
else {
make_zero64(p->p_cpu_time_left);
}
#endif
}
/*
* This function is called only if we switch from kernel to user or idle
* or back. Therefore this is a perfect location to place the big kernel
* lock which will hopefully disappear soon.
*
* If we stop accounting for KERNEL we must unlock the BKL. If account
* for IDLE we must not hold the lock
*/
if (p == proc_addr(KERNEL))
BKL_UNLOCK();
else
BKL_LOCK();
}
PUBLIC void context_stop_idle(void)
{
context_stop(proc_addr(IDLE));
}
PUBLIC u64_t ms_2_cpu_time(unsigned ms)
{
return mul64u(tsc_per_ms[cpuid], ms);
}