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SMP - BKL statistics

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- pressing 'B' on the serial cnsole prints statistics for BKL per cpu.

- 'b' resets the counters

- it presents number of cycles each CPU spends in kernel, how many
  cycyles it spends spinning while waiting for the BKL

- it shows optimistic estimation in how many cases we get the lock
  immediately without spinning. As the test is not atomic the lock may
  be already held by some other cpu before we actually try to acquire
  it.
This commit is contained in:
Tomas Hruby 2010-09-15 14:10:37 +00:00
parent 93b9873a56
commit c554aef0e1
3 changed files with 56 additions and 1 deletions
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18
kernel/arch/i386/arch_clock.c
View file

@ -217,9 +217,25 @@ PUBLIC void context_stop(struct proc * p)
p->p_cycles = add64(p->p_cycles, sub64(tsc, *__tsc_ctr_switch));
BKL_UNLOCK();
} else {
u64_t bkl_tsc, tmp;
unsigned cpu = cpuid;
atomic_t succ;
read_tsc_64(&bkl_tsc);
/* this only gives a good estimate */
succ = big_kernel_lock.val;
BKL_LOCK();
read_tsc_64(&tsc);
p->p_cycles = add64(p->p_cycles, sub64(tsc, *__tsc_ctr_switch));
bkl_ticks[cpu] = add64(bkl_ticks[cpu], sub64(tsc, bkl_tsc));
bkl_tries[cpu]++;
bkl_succ[cpu] += !(!(succ == 0));
tmp = sub64(tsc, *__tsc_ctr_switch);
kernel_ticks[cpu] = add64(kernel_ticks[cpu], tmp);
p->p_cycles = add64(p->p_cycles, tmp);
}
*__tsc_ctr_switch = tsc;

33
kernel/arch/i386/arch_system.c
View file

@ -420,6 +420,31 @@ PRIVATE void ser_dump_segs(void)
}
}
#ifdef CONFIG_SMP
PRIVATE void dump_bkl_usage(void)
{
unsigned cpu;
printf("--- BKL usage ---\n");
for (cpu = 0; cpu < ncpus; cpu++) {
printf("cpu %3d kernel ticks 0x%x%08x bkl ticks 0x%x%08x succ %d tries %d\n", cpu,
kernel_ticks[cpu].hi, kernel_ticks[cpu].lo,
bkl_ticks[cpu].hi, bkl_ticks[cpu].lo,
bkl_succ[cpu], bkl_tries[cpu]);
}
}
PRIVATE void reset_bkl_usage(void)
{
unsigned cpu;
memset(kernel_ticks, 0, sizeof(kernel_ticks));
memset(bkl_ticks, 0, sizeof(bkl_ticks));
memset(bkl_tries, 0, sizeof(bkl_tries));
memset(bkl_succ, 0, sizeof(bkl_succ));
}
#endif
PRIVATE void ser_debug(const int c)
{
serial_debug_active = 1;
@ -429,6 +454,14 @@ PRIVATE void ser_debug(const int c)
case 'Q':
minix_shutdown(NULL);
NOT_REACHABLE;
#ifdef CONFIG_SMP
case 'B':
dump_bkl_usage();
break;
case 'b':
reset_bkl_usage();
break;
#endif
case '1':
ser_dump_proc();
break;

6
kernel/glo.h
View file

@ -80,4 +80,10 @@ extern struct segdesc_s gdt[]; /* global descriptor table */
EXTERN volatile int serial_debug_active;
/* BKL stats */
EXTERN u64_t kernel_ticks[CONFIG_MAX_CPUS];
EXTERN u64_t bkl_ticks[CONFIG_MAX_CPUS];
EXTERN unsigned bkl_tries[CONFIG_MAX_CPUS];
EXTERN unsigned bkl_succ[CONFIG_MAX_CPUS];
#endif /* GLO_H */