From 2ac0d98fd624ae50f5e6ae9c800977a9dbbfcde6 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 28 Jul 2011 04:00:47 +0200 Subject: [PATCH] nohz: Make nohz API agnostic against idle ticks cputime accounting When the timer tick fires, it accounts the new jiffy as either part of system, user or idle time. This is how we record the cputime statistics. But when the tick is stopped from the idle task, we still need to record the number of jiffies spent tickless until we restart the tick and fall back to traditional tick-based cputime accounting. To do this, we take a snapshot of jiffies when the tick is stopped and compute the difference against the new value of jiffies when the tick is restarted. Then we account this whole difference to the idle cputime. However we are preparing to be able to stop the tick from other places than idle. So this idle time accounting needs to be performed from the callers of nohz APIs, not from the nohz APIs themselves because we now want them to be agnostic against places that stop/restart tick. Therefore, we pull the tickless idle time accounting out of generic nohz helpers up to idle entry/exit callers. Signed-off-by: Frederic Weisbecker Cc: Alessio Igor Bogani Cc: Andrew Morton Cc: Avi Kivity Cc: Chris Metcalf Cc: Christoph Lameter Cc: Daniel Lezcano Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: Ingo Molnar Cc: Kevin Hilman Cc: Max Krasnyansky Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Stephen Hemminger Cc: Steven Rostedt Cc: Sven-Thorsten Dietrich Cc: Thomas Gleixner --- kernel/time/tick-sched.c | 37 ++++++++++++++++++++++--------------- 1 file changed, 22 insertions(+), 15 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 81409bba2425..911834b33b8a 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -402,7 +402,6 @@ static void tick_nohz_stop_sched_tick(struct tick_sched *ts, ktime_t now) ts->idle_tick = hrtimer_get_expires(&ts->sched_timer); ts->tick_stopped = 1; - ts->idle_jiffies = last_jiffies; } ts->idle_sleeps++; @@ -445,9 +444,13 @@ out: static void __tick_nohz_idle_enter(struct tick_sched *ts) { ktime_t now; + int was_stopped = ts->tick_stopped; now = tick_nohz_start_idle(smp_processor_id(), ts); tick_nohz_stop_sched_tick(ts, now); + + if (!was_stopped && ts->tick_stopped) + ts->idle_jiffies = ts->last_jiffies; } /** @@ -548,15 +551,25 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) { -#ifndef CONFIG_VIRT_CPU_ACCOUNTING - unsigned long ticks; -#endif /* Update jiffies first */ select_nohz_load_balancer(0); tick_do_update_jiffies64(now); update_cpu_load_nohz(); + touch_softlockup_watchdog(); + /* + * Cancel the scheduled timer and restore the tick + */ + ts->tick_stopped = 0; + ts->idle_exittime = now; + + tick_nohz_restart(ts, now); +} + +static void tick_nohz_account_idle_ticks(struct tick_sched *ts) +{ #ifndef CONFIG_VIRT_CPU_ACCOUNTING + unsigned long ticks; /* * We stopped the tick in idle. Update process times would miss the * time we slept as update_process_times does only a 1 tick @@ -569,15 +582,6 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) if (ticks && ticks < LONG_MAX) account_idle_ticks(ticks); #endif - - touch_softlockup_watchdog(); - /* - * Cancel the scheduled timer and restore the tick - */ - ts->tick_stopped = 0; - ts->idle_exittime = now; - - tick_nohz_restart(ts, now); } /** @@ -605,8 +609,10 @@ void tick_nohz_idle_exit(void) if (ts->idle_active) tick_nohz_stop_idle(cpu, now); - if (ts->tick_stopped) + if (ts->tick_stopped) { tick_nohz_restart_sched_tick(ts, now); + tick_nohz_account_idle_ticks(ts); + } local_irq_enable(); } @@ -811,7 +817,8 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) */ if (ts->tick_stopped) { touch_softlockup_watchdog(); - ts->idle_jiffies++; + if (idle_cpu(cpu)) + ts->idle_jiffies++; } update_process_times(user_mode(regs)); profile_tick(CPU_PROFILING);