If the task is not running, run_posix_cpu_timers has nothing
to elapsed, so spare IPI in that case.
Suggested-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com>
Index: linux-2.6/kernel/sched/core.c
===================================================================
--- linux-2.6.orig/kernel/sched/core.c
+++ linux-2.6/kernel/sched/core.c
@@ -9182,3 +9182,9 @@ void call_trace_sched_update_nr_running(
{
trace_sched_update_nr_running_tp(rq, count);
}
+
+bool task_on_rq(struct task_struct *p)
+{
+ return p->on_rq == TASK_ON_RQ_QUEUED;
+}
+
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -232,6 +232,8 @@ extern void io_schedule_finish(int token
extern long io_schedule_timeout(long timeout);
extern void io_schedule(void);
+extern bool task_on_rq(struct task_struct *p);
+
/**
* struct prev_cputime - snapshot of system and user cputime
* @utime: time spent in user mode
Index: linux-2.6/kernel/time/tick-sched.c
===================================================================
--- linux-2.6.orig/kernel/time/tick-sched.c
+++ linux-2.6/kernel/time/tick-sched.c
@@ -324,8 +324,6 @@ void tick_nohz_full_kick_cpu(int cpu)
static void tick_nohz_kick_task(struct task_struct *tsk)
{
- int cpu = task_cpu(tsk);
-
/*
* If the task concurrently migrates to another cpu,
* we guarantee it sees the new tick dependency upon
@@ -340,6 +338,23 @@ static void tick_nohz_kick_task(struct t
* tick_nohz_task_switch() smp_mb() (atomic_fetch_or())
* LOAD p->tick_dep_mask LOAD p->cpu
*/
+ int cpu = task_cpu(tsk);
+
+ /*
+ * If the task is not running, run_posix_cpu_timers
+ * has nothing to elapsed, can spare IPI in that
+ * case.
+ *
+ * activate_task() STORE p->tick_dep_mask
+ * STORE p->task_on_rq
+ * __schedule() (switch to task 'p') smp_mb() (atomic_fetch_or())
+ * LOCK rq->lock LOAD p->task_on_rq
+ * smp_mb__after_spin_lock()
+ * tick_nohz_task_switch()
+ * LOAD p->tick_dep_mask
+ */
+ if (!task_on_rq(tsk))
+ return;
preempt_disable();
if (cpu_online(cpu))
