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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 <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2012-02-23 17:13:19 -08:00 committed by Paul E. McKenney
parent 2fdbb31b66
commit 2ee3dc8066
1 changed files with 12 additions and 28 deletions
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40
kernel/rcutree_plugin.h
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@ -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 */