Commit d1e43fa5 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

nohz: Ensure full dynticks CPUs are RCU nocbs 



We need full dynticks CPU to also be RCU nocb so
that we don't have to keep the tick to handle RCU
callbacks.

Make sure the range passed to nohz_full= boot
parameter is a subset of rcu_nocbs=

The CPUs that fail to meet this requirement will be
excluded from the nohz_full range. This is checked
early in boot time, before any CPU has the opportunity
to stop its tick.

Suggested-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Reviewed-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
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: 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 0453b435

Documentation/kernel-parameters.txt

+2 −0
Original line number Diff line number Diff line
@@ -1918,6 +1918,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			the specified list of CPUs whose tick will be stopped

			whenever possible. The boot CPU will be forced outside

			the range to maintain the timekeeping.

			The CPUs in this range must also be included in the

			rcu_nocbs= set.



	noiotrap	[SH] Disables trapped I/O port accesses.

include/linux/rcupdate.h

+7 −0
Original line number Diff line number Diff line
@@ -999,4 +999,11 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) 
#define kfree_rcu(ptr, rcu_head)					\

	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))



#ifdef CONFIG_RCU_NOCB_CPU

extern bool rcu_is_nocb_cpu(int cpu);

#else

static inline bool rcu_is_nocb_cpu(int cpu) { return false; }

#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */





#endif /* __LINUX_RCUPDATE_H */

include/linux/tick.h

+2 −0
Original line number Diff line number Diff line
@@ -158,8 +158,10 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; } 
# endif /* !CONFIG_NO_HZ_COMMON */



#ifdef CONFIG_NO_HZ_FULL

extern void tick_nohz_init(void);

extern int tick_nohz_full_cpu(int cpu);

#else

static inline void tick_nohz_init(void) { }

static inline int tick_nohz_full_cpu(int cpu) { return 0; }

#endif

init/main.c

+1 −0
Original line number Diff line number Diff line
@@ -547,6 +547,7 @@ asmlinkage void __init start_kernel(void) 
	idr_init_cache();

	perf_event_init();

	rcu_init();

	tick_nohz_init();

	radix_tree_init();

	/* init some links before init_ISA_irqs() */

	early_irq_init();

kernel/rcutree.c

+3 −3
Original line number Diff line number Diff line
@@ -1695,7 +1695,7 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp, 
			  struct rcu_node *rnp, struct rcu_data *rdp)

{

	/* No-CBs CPUs do not have orphanable callbacks. */

	if (is_nocb_cpu(rdp->cpu))

	if (rcu_is_nocb_cpu(rdp->cpu))

		return;



	/*
@@ -2757,10 +2757,10 @@ static void _rcu_barrier(struct rcu_state *rsp) 
	 * corresponding CPU's preceding callbacks have been invoked.

	 */

	for_each_possible_cpu(cpu) {

		if (!cpu_online(cpu) && !is_nocb_cpu(cpu))

		if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))

			continue;

		rdp = per_cpu_ptr(rsp->rda, cpu);

		if (is_nocb_cpu(cpu)) {

		if (rcu_is_nocb_cpu(cpu)) {

			_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,

					   rsp->n_barrier_done);

			atomic_inc(&rsp->barrier_cpu_count);

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