On a NO_HZ system, there may be an arbitrarily long delay between ticks on a CPU. When we're disabling ticks for a CPU, also disable the softlockup watchdog timer. This makes the touch_softlockup_watchdog() interface redundant; if a piece of code knows its going to be holding off timer interrupts long enough to trigger the watchdog, then it may as well simply temporarily disable the timer. Signed-off-by: Jeremy Fitzhardinge Cc: Ingo Molnar Cc: Thomas Gleixner Cc: john stultz Cc: Zachary Amsden Cc: James Morris Cc: Dan Hecht Cc: Paul Mackerras Cc: Martin Schwidefsky Cc: Prarit Bhargava Cc: Chris Lalancette Cc: Eric Dumazet --- include/linux/sched.h | 25 +++++++++++++++++ kernel/softlockup.c | 67 ++++++++++++++++++++++++++++++++++++++++++---- kernel/time/tick-sched.c | 34 ++++++++++------------- 3 files changed, 102 insertions(+), 24 deletions(-) =================================================================== --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -232,12 +232,37 @@ extern void scheduler_tick(void); extern void scheduler_tick(void); #ifdef CONFIG_DETECT_SOFTLOCKUP +/* A scheduler tick on this CPU */ extern void softlockup_tick(void); + +/* Scheduler is disabling/re-enabling ticks on this CPU */ +extern void softlockup_tick_disable(void); +extern void softlockup_tick_enable(void); + +/* Some code wants to temporarily disable the watchdog */ +extern int softlockup_disable(void); +extern void softlockup_enable(int state); + extern void spawn_softlockup_task(void); extern void touch_softlockup_watchdog(void); #else static inline void softlockup_tick(void) { +} +static inline void softlockup_tick_disable(void) +{ +} +static inline void softlockup_tick_enable(void) +{ +} +static inline int softlockup_disable(void) +{ + preempt_disable(); + return 0; +} +static inline void softlockup_enable(int state) +{ + preempt_enable(); } static inline void spawn_softlockup_task(void) { =================================================================== --- a/kernel/softlockup.c +++ b/kernel/softlockup.c @@ -20,6 +20,7 @@ static DEFINE_PER_CPU(unsigned long, tou static DEFINE_PER_CPU(unsigned long, touch_timestamp); static DEFINE_PER_CPU(unsigned long, print_timestamp); static DEFINE_PER_CPU(struct task_struct *, watchdog_task); +static DEFINE_PER_CPU(int, enabled); static int did_panic = 0; @@ -45,11 +46,65 @@ static unsigned long get_timestamp(void) return sched_clock() >> 30; /* 2^30 ~= 10^9 */ } -void touch_softlockup_watchdog(void) +void inline touch_softlockup_watchdog(void) { __raw_get_cpu_var(touch_timestamp) = get_timestamp(); } EXPORT_SYMBOL(touch_softlockup_watchdog); + +/* + * Disable the watchdog on this CPU. This is called directly by the + * scheduler to tell us it's going tickless. + */ +void inline softlockup_tick_disable(void) +{ + __get_cpu_var(enabled) = 0; +} + +/* + * Disable the watchdog for this CPU, returning the current state to + * allow nesting. Returns with preemptio disabled, since we can't + * switch CPUs before we re-enable the watchdog (also, if we're + * worried about getting watchdog timeouts, we're not scheduling). + */ +int softlockup_disable(void) +{ + int ret; + + preempt_disable(); + + ret = __get_cpu_var(enabled); + softlockup_tick_disable(); + + return ret; +} +EXPORT_SYMBOL(softlockup_disable); + +/* + * Re-enable the watchdog on this CPU. Called directly by the + * scheduler to tell us ticks are resuming. + */ +void inline softlockup_tick_enable(void) +{ + __get_cpu_var(enabled) = 1; +} + +/* + * Returns softlockup watchdog state to before the last per-cpu + * disable. + */ +void softlockup_enable(int state) +{ + if (state) { + touch_softlockup_watchdog(); + /* update timestamp before enable */ + barrier(); + softlockup_tick_enable(); + } + + preempt_enable(); +} +EXPORT_SYMBOL(softlockup_enable); /* * This callback runs from the timer interrupt, and checks @@ -62,8 +117,8 @@ void softlockup_tick(void) unsigned long print_timestamp; unsigned long now; - /* watchdog task hasn't updated timestamp yet */ - if (touch_timestamp == 0) + /* return if not enabled */ + if (!__get_cpu_var(enabled)) return; print_timestamp = __get_cpu_var(print_timestamp); @@ -108,8 +163,8 @@ static int watchdog(void * __bind_cpu) sched_setscheduler(current, SCHED_FIFO, ¶m); current->flags |= PF_NOFREEZE; - /* initialize timestamp */ - touch_softlockup_watchdog(); + /* enable on this cpu */ + softlockup_tick_enable(); /* * Run briefly once per second to reset the softlockup timestamp. @@ -122,6 +177,8 @@ static int watchdog(void * __bind_cpu) touch_softlockup_watchdog(); schedule(); } + + softlockup_tick_disable(); return 0; } =================================================================== --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -228,6 +228,8 @@ void tick_nohz_stop_sched_tick(void) ts->idle_tick = ts->sched_timer.expires; ts->tick_stopped = 1; ts->idle_jiffies = last_jiffies; + + softlockup_tick_disable(); } /* * calculate the expiry time for the next timer wheel @@ -255,6 +257,7 @@ void tick_nohz_stop_sched_tick(void) cpu_clear(cpu, nohz_cpu_mask); } raise_softirq_irqoff(TIMER_SOFTIRQ); + out: ts->next_jiffies = next_jiffies; ts->last_jiffies = last_jiffies; @@ -311,6 +314,8 @@ void tick_nohz_restart_sched_tick(void) ts->tick_stopped = 0; hrtimer_cancel(&ts->sched_timer); ts->sched_timer.expires = ts->idle_tick; + + softlockup_tick_enable(); while (1) { /* Forward the time to expire in the future */ @@ -355,17 +360,12 @@ static void tick_nohz_handler(struct clo tick_do_update_jiffies64(now); /* - * When we are idle and the tick is stopped, we have to touch - * the watchdog as we might not schedule for a really long - * time. This happens on complete idle SMP systems while - * waiting on the login prompt. We also increment the "start - * of idle" jiffy stamp so the idle accounting adjustment we - * do when we go busy again does not account too much ticks. - */ - if (ts->tick_stopped) { - touch_softlockup_watchdog(); + * Increment the "start of idle" jiffy stamp so the idle + * accounting adjustment we do when we go busy again does not + * account too much ticks. + */ + if (ts->tick_stopped) ts->idle_jiffies++; - } update_process_times(user_mode(regs)); profile_tick(CPU_PROFILING); @@ -450,17 +450,12 @@ static enum hrtimer_restart tick_sched_t */ if (regs) { /* - * When we are idle and the tick is stopped, we have to touch - * the watchdog as we might not schedule for a really long - * time. This happens on complete idle SMP systems while - * waiting on the login prompt. We also increment the "start of - * idle" jiffy stamp so the idle accounting adjustment we do - * when we go busy again does not account too much ticks. + * Increment the "start of idle" jiffy stamp so the + * idle accounting adjustment we do when we go busy + * again does not account too much ticks. */ - if (ts->tick_stopped) { - touch_softlockup_watchdog(); + if (ts->tick_stopped) ts->idle_jiffies++; - } /* * update_process_times() might take tasklist_lock, hence * drop the base lock. sched-tick hrtimers are per-CPU and @@ -522,6 +517,7 @@ void tick_cancel_sched_timer(int cpu) if (ts->sched_timer.base) hrtimer_cancel(&ts->sched_timer); ts->tick_stopped = 0; + softlockup_tick_enable(); ts->nohz_mode = NOHZ_MODE_INACTIVE; } #endif /* HIGH_RES_TIMERS */ -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/