From cc584b213f252bf698849cf4be2377cd3ec7501a Mon Sep 17 00:00:00 2001 From: Arjan van de Ven Date: Mon, 1 Sep 2008 15:02:30 -0700 Subject: hrtimer: convert kernel/* to the new hrtimer apis In order to be able to do range hrtimers we need to use accessor functions to the "expire" member of the hrtimer struct. This patch converts kernel/* to these accessors. Signed-off-by: Arjan van de Ven --- kernel/time/tick-sched.c | 21 ++++++++++----------- 1 file changed, 10 insertions(+), 11 deletions(-) (limited to 'kernel/time/tick-sched.c') diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index a87b0468568b..b33be61c0f6b 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -288,7 +288,7 @@ void tick_nohz_stop_sched_tick(int inidle) goto out; } - ts->idle_tick = ts->sched_timer.expires; + ts->idle_tick = hrtimer_get_expires(&ts->sched_timer); ts->tick_stopped = 1; ts->idle_jiffies = last_jiffies; rcu_enter_nohz(); @@ -419,21 +419,21 @@ void tick_nohz_restart_sched_tick(void) ts->tick_stopped = 0; ts->idle_exittime = now; hrtimer_cancel(&ts->sched_timer); - ts->sched_timer.expires = ts->idle_tick; + hrtimer_set_expires(&ts->sched_timer, ts->idle_tick); while (1) { /* Forward the time to expire in the future */ hrtimer_forward(&ts->sched_timer, now, tick_period); if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { - hrtimer_start(&ts->sched_timer, - ts->sched_timer.expires, + hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS); /* Check, if the timer was already in the past */ if (hrtimer_active(&ts->sched_timer)) break; } else { - if (!tick_program_event(ts->sched_timer.expires, 0)) + if (!tick_program_event( + hrtimer_get_expires(&ts->sched_timer), 0)) break; } /* Update jiffies and reread time */ @@ -446,7 +446,7 @@ void tick_nohz_restart_sched_tick(void) static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now) { hrtimer_forward(&ts->sched_timer, now, tick_period); - return tick_program_event(ts->sched_timer.expires, 0); + return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0); } /* @@ -529,7 +529,7 @@ static void tick_nohz_switch_to_nohz(void) next = tick_init_jiffy_update(); for (;;) { - ts->sched_timer.expires = next; + hrtimer_set_expires(&ts->sched_timer, next); if (!tick_program_event(next, 0)) break; next = ktime_add(next, tick_period); @@ -625,16 +625,15 @@ void tick_setup_sched_timer(void) ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ; /* Get the next period (per cpu) */ - ts->sched_timer.expires = tick_init_jiffy_update(); + hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); offset = ktime_to_ns(tick_period) >> 1; do_div(offset, num_possible_cpus()); offset *= smp_processor_id(); - ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset); + hrtimer_add_expires_ns(&ts->sched_timer, offset); for (;;) { hrtimer_forward(&ts->sched_timer, now, tick_period); - hrtimer_start(&ts->sched_timer, ts->sched_timer.expires, - HRTIMER_MODE_ABS); + hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS); /* Check, if the timer was already in the past */ if (hrtimer_active(&ts->sched_timer)) break; -- cgit v1.2.2 From 719254faa17ffedc87ba0fadb9b34e535c9758d5 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 17 Oct 2008 09:59:47 +0200 Subject: NOHZ: unify the nohz function calls in irq_enter() We have two separate nohz function calls in irq_enter() for no good reason. Just call a single NOHZ function from irq_enter() and call the bits in the tick code. Signed-off-by: Thomas Gleixner --- kernel/time/tick-sched.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) (limited to 'kernel/time/tick-sched.c') diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index b711ffcb106c..fdcf3f93bb8d 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -155,7 +155,7 @@ void tick_nohz_update_jiffies(void) touch_softlockup_watchdog(); } -void tick_nohz_stop_idle(int cpu) +static void tick_nohz_stop_idle(int cpu) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); @@ -558,6 +558,17 @@ static inline void tick_nohz_switch_to_nohz(void) { } #endif /* NO_HZ */ +/* + * Called from irq_enter to notify about the possible interruption of idle() + */ +void tick_check_idle(int cpu) +{ +#ifdef CONFIG_NO_HZ + tick_nohz_stop_idle(cpu); + tick_nohz_update_jiffies(); +#endif +} + /* * High resolution timer specific code */ -- cgit v1.2.2 From c34bec5a44e9486597d78e7a686b2f9088a0564c Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 17 Oct 2008 10:04:34 +0200 Subject: NOHZ: split tick_nohz_restart_sched_tick() Split out the clock event device reprogramming. Preparatory patch. Signed-off-by: Thomas Gleixner --- kernel/time/tick-sched.c | 49 ++++++++++++++++++++++++++---------------------- 1 file changed, 27 insertions(+), 22 deletions(-) (limited to 'kernel/time/tick-sched.c') diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index fdcf3f93bb8d..7aedf4343539 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -377,6 +377,32 @@ ktime_t tick_nohz_get_sleep_length(void) return ts->sleep_length; } +static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) +{ + hrtimer_cancel(&ts->sched_timer); + ts->sched_timer.expires = ts->idle_tick; + + while (1) { + /* Forward the time to expire in the future */ + hrtimer_forward(&ts->sched_timer, now, tick_period); + + if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { + hrtimer_start(&ts->sched_timer, + ts->sched_timer.expires, + HRTIMER_MODE_ABS); + /* Check, if the timer was already in the past */ + if (hrtimer_active(&ts->sched_timer)) + break; + } else { + if (!tick_program_event(ts->sched_timer.expires, 0)) + break; + } + /* Update jiffies and reread time */ + tick_do_update_jiffies64(now); + now = ktime_get(); + } +} + /** * tick_nohz_restart_sched_tick - restart the idle tick from the idle task * @@ -430,28 +456,7 @@ void tick_nohz_restart_sched_tick(void) */ ts->tick_stopped = 0; ts->idle_exittime = now; - hrtimer_cancel(&ts->sched_timer); - ts->sched_timer.expires = ts->idle_tick; - - while (1) { - /* Forward the time to expire in the future */ - hrtimer_forward(&ts->sched_timer, now, tick_period); - - if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { - hrtimer_start(&ts->sched_timer, - ts->sched_timer.expires, - HRTIMER_MODE_ABS); - /* Check, if the timer was already in the past */ - if (hrtimer_active(&ts->sched_timer)) - break; - } else { - if (!tick_program_event(ts->sched_timer.expires, 0)) - break; - } - /* Update jiffies and reread time */ - tick_do_update_jiffies64(now); - now = ktime_get(); - } + tick_nohz_restart(ts, now); local_irq_enable(); } -- cgit v1.2.2 From fb02fbc14d17837b4b7b02dbb36142c16a7bf208 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 17 Oct 2008 10:01:23 +0200 Subject: NOHZ: restart tick device from irq_enter() We did not restart the tick device from irq_enter() to avoid double reprogramming and extra events in the return immediate to idle case. But long lasting softirqs can lead to a situation where jiffies become stale: idle() tick stopped (reprogrammed to next pending timer) halt() interrupt jiffies updated from irq_enter() interrupt handler softirq function 1 runs 20ms softirq function 2 arms a 10ms timer with a stale jiffies value jiffies updated from irq_exit() timer wheel has now an already expired timer (the one added in function 2) timer fires and timer softirq runs This was discovered when debugging a timer problem which happend only when the ath5k driver is active. The debugging proved that there is a softirq function running for more than 20ms, which is a bug by itself. To solve this we restart the tick timer right from irq_enter(), but do not go through the other functions which are necessary to return from idle when need_resched() is set. Reported-by: Elias Oltmanns Signed-off-by: Thomas Gleixner Tested-by: Elias Oltmanns --- kernel/time/tick-sched.c | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-) (limited to 'kernel/time/tick-sched.c') diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 7aedf4343539..0581c11fe6c6 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -508,10 +508,6 @@ static void tick_nohz_handler(struct clock_event_device *dev) update_process_times(user_mode(regs)); profile_tick(CPU_PROFILING); - /* Do not restart, when we are in the idle loop */ - if (ts->tick_stopped) - return; - while (tick_nohz_reprogram(ts, now)) { now = ktime_get(); tick_do_update_jiffies64(now); @@ -557,6 +553,27 @@ static void tick_nohz_switch_to_nohz(void) smp_processor_id()); } +/* + * When NOHZ is enabled and the tick is stopped, we need to kick the + * tick timer from irq_enter() so that the jiffies update is kept + * alive during long running softirqs. That's ugly as hell, but + * correctness is key even if we need to fix the offending softirq in + * the first place. + * + * Note, this is different to tick_nohz_restart. We just kick the + * timer and do not touch the other magic bits which need to be done + * when idle is left. + */ +static void tick_nohz_kick_tick(int cpu) +{ + struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); + + if (!ts->tick_stopped) + return; + + tick_nohz_restart(ts, ktime_get()); +} + #else static inline void tick_nohz_switch_to_nohz(void) { } @@ -568,9 +585,11 @@ static inline void tick_nohz_switch_to_nohz(void) { } */ void tick_check_idle(int cpu) { + tick_check_oneshot_broadcast(cpu); #ifdef CONFIG_NO_HZ tick_nohz_stop_idle(cpu); tick_nohz_update_jiffies(); + tick_nohz_kick_tick(cpu); #endif } @@ -627,10 +646,6 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) profile_tick(CPU_PROFILING); } - /* Do not restart, when we are in the idle loop */ - if (ts->tick_stopped) - return HRTIMER_NORESTART; - hrtimer_forward(timer, now, tick_period); return HRTIMER_RESTART; -- cgit v1.2.2 From c4bd822e7b12a9008241d76db45b665f2fef180c Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 21 Oct 2008 20:17:35 +0200 Subject: NOHZ: fix thinko in the timer restart code path commit fb02fbc14d17837b4b7b02dbb36142c16a7bf208 (NOHZ: restart tick device from irq_enter()) solves the problem of stale jiffies when long running softirqs happen in a long idle sleep period, but it has a major thinko in it: When the interrupt which came in _is_ the timer interrupt which should expire ts->sched_timer then we cancel and rearm the timer _before_ it gets expired in hrtimer_interrupt() to the next period. That means the call back function is not called. This game can go on for ever :( Prevent this by making sure to only rearm the timer when the expiry time is more than one tick_period away. Otherwise keep it running as it is either already expired or will expiry at the right point to update jiffies. Signed-off-by: Thomas Gleixner Tested-by: Venkatesch Pallipadi --- kernel/time/tick-sched.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'kernel/time/tick-sched.c') diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 0581c11fe6c6..727c1ae0517a 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -567,11 +567,21 @@ static void tick_nohz_switch_to_nohz(void) static void tick_nohz_kick_tick(int cpu) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); + ktime_t delta, now; if (!ts->tick_stopped) return; - tick_nohz_restart(ts, ktime_get()); + /* + * Do not touch the tick device, when the next expiry is either + * already reached or less/equal than the tick period. + */ + now = ktime_get(); + delta = ktime_sub(ts->sched_timer.expires, now); + if (delta.tv64 <= tick_period.tv64) + return; + + tick_nohz_restart(ts, now); } #else -- cgit v1.2.2