From 2ee3dc80660ac8285a37e662fd91b2e45c46f06a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 23 Feb 2012 17:13:19 -0800 Subject: [PATCH] rcu: Make RCU_FAST_NO_HZ use timer rather than hrtimer The RCU_FAST_NO_HZ facility uses an hrtimer to wake up a CPU when it is allowed to go into dyntick-idle mode, which is almost always cancelled soon after. This is not what hrtimers are good at, so this commit switches to the timer wheel. Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 40 ++++++++++++---------------------------- 1 file changed, 12 insertions(+), 28 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 1e561ab952a..0f007b363db 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1980,9 +1980,7 @@ static void rcu_prepare_for_idle(int cpu) static DEFINE_PER_CPU(int, rcu_dyntick_drain); static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); -static DEFINE_PER_CPU(struct hrtimer, rcu_idle_gp_timer); -static ktime_t rcu_idle_gp_wait; /* If some non-lazy callbacks. */ -static ktime_t rcu_idle_lazy_gp_wait; /* If only lazy callbacks. */ +static DEFINE_PER_CPU(struct timer_list, rcu_idle_gp_timer); /* * Allow the CPU to enter dyntick-idle mode if either: (1) There are no @@ -2051,10 +2049,9 @@ static bool rcu_cpu_has_nonlazy_callbacks(int cpu) * real work is done upon re-entry to idle, or by the next scheduling-clock * interrupt should idle not be re-entered. */ -static enum hrtimer_restart rcu_idle_gp_timer_func(struct hrtimer *hrtp) +static void rcu_idle_gp_timer_func(unsigned long unused) { trace_rcu_prep_idle("Timer"); - return HRTIMER_NORESTART; } /* @@ -2062,19 +2059,8 @@ static enum hrtimer_restart rcu_idle_gp_timer_func(struct hrtimer *hrtp) */ static void rcu_prepare_for_idle_init(int cpu) { - static int firsttime = 1; - struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu); - - hrtimer_init(hrtp, CLOCK_MONOTONIC, HRTIMER_MODE_REL); - hrtp->function = rcu_idle_gp_timer_func; - if (firsttime) { - unsigned int upj = jiffies_to_usecs(RCU_IDLE_GP_DELAY); - - rcu_idle_gp_wait = ns_to_ktime(upj * (u64)1000); - upj = jiffies_to_usecs(RCU_IDLE_LAZY_GP_DELAY); - rcu_idle_lazy_gp_wait = ns_to_ktime(upj * (u64)1000); - firsttime = 0; - } + setup_timer(&per_cpu(rcu_idle_gp_timer, cpu), + rcu_idle_gp_timer_func, 0); } /* @@ -2084,7 +2070,7 @@ static void rcu_prepare_for_idle_init(int cpu) */ static void rcu_cleanup_after_idle(int cpu) { - hrtimer_cancel(&per_cpu(rcu_idle_gp_timer, cpu)); + del_timer(&per_cpu(rcu_idle_gp_timer, cpu)); trace_rcu_prep_idle("Cleanup after idle"); } @@ -2141,11 +2127,11 @@ static void rcu_prepare_for_idle(int cpu) per_cpu(rcu_dyntick_drain, cpu) = 0; per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; if (rcu_cpu_has_nonlazy_callbacks(cpu)) - hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu), - rcu_idle_gp_wait, HRTIMER_MODE_REL); + mod_timer(&per_cpu(rcu_idle_gp_timer, cpu), + jiffies + RCU_IDLE_GP_DELAY); else - hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu), - rcu_idle_lazy_gp_wait, HRTIMER_MODE_REL); + mod_timer(&per_cpu(rcu_idle_gp_timer, cpu), + jiffies + RCU_IDLE_LAZY_GP_DELAY); return; /* Nothing more to do immediately. */ } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { /* We have hit the limit, so time to give up. */ @@ -2193,14 +2179,12 @@ static void rcu_prepare_for_idle(int cpu) static void print_cpu_stall_fast_no_hz(char *cp, int cpu) { - struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu); + struct timer_list *tltp = &per_cpu(rcu_idle_gp_timer, cpu); - sprintf(cp, "drain=%d %c timer=%lld", + sprintf(cp, "drain=%d %c timer=%lu", per_cpu(rcu_dyntick_drain, cpu), per_cpu(rcu_dyntick_holdoff, cpu) == jiffies ? 'H' : '.', - hrtimer_active(hrtp) - ? ktime_to_us(hrtimer_get_remaining(hrtp)) - : -1); + timer_pending(tltp) ? tltp->expires - jiffies : -1); } #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ -- 2.41.0