Commit ce831b38 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

sched: New helper to prevent from stopping the tick in full dynticks 



Provide a new helper to be called from the full dynticks engine
before stopping the tick in order to make sure we don't stop
it when there is more than one task running on the CPU.

This way we make sure that the tick stays alive to maintain
fairness.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
parent 9f3660c2

include/linux/sched.h

+6 −0
Original line number Diff line number Diff line
@@ -1856,6 +1856,12 @@ extern void wake_up_nohz_cpu(int cpu); 
static inline void wake_up_nohz_cpu(int cpu) { }

#endif



#ifdef CONFIG_NO_HZ_FULL

extern bool sched_can_stop_tick(void);

#else

static inline bool sched_can_stop_tick(void) { return false; }

#endif



#ifdef CONFIG_SCHED_AUTOGROUP

extern void sched_autogroup_create_attach(struct task_struct *p);

extern void sched_autogroup_detach(struct task_struct *p);

kernel/sched/core.c

+18 −0
Original line number Diff line number Diff line
@@ -650,6 +650,24 @@ static inline bool got_nohz_idle_kick(void) 


#endif /* CONFIG_NO_HZ_COMMON */



#ifdef CONFIG_NO_HZ_FULL

bool sched_can_stop_tick(void)

{

       struct rq *rq;



       rq = this_rq();



       /* Make sure rq->nr_running update is visible after the IPI */

       smp_rmb();



       /* More than one running task need preemption */

       if (rq->nr_running > 1)

               return false;



       return true;

}

#endif /* CONFIG_NO_HZ_FULL */



void sched_avg_update(struct rq *rq)

{

	s64 period = sched_avg_period();

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