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Commit 21871d7e authored by Clark Williams's avatar Clark Williams Committed by Paul E. McKenney
Browse files

rcu: Unify boost and kthread priorities 



Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
threads (rcub/n).

Also, create the module_parameter rcutree.kthread_prio to be used on
the kernel command line at boot to set a new value (rcutree.kthread_prio=N).

Signed-off-by: default avatarClark Williams <clark.williams@gmail.com>
[ paulmck: Ported to rcu/dev, applied Paul Bolle and Peter Zijlstra feedback. ]
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent e0775cef

Documentation/kernel-parameters.txt

+7 −0
Original line number Diff line number Diff line
@@ -2922,6 +2922,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			quiescent states.  Units are jiffies, minimum

			value is one, and maximum value is HZ.



	rcutree.kthread_prio= 	 [KNL,BOOT]

			Set the SCHED_FIFO priority of the RCU

			per-CPU kthreads (rcuc/N). This value is also

			used for the priority of the RCU boost threads

			(rcub/N). Valid values are 1-99 and the default

			is 1 (the least-favored priority).



	rcutree.rcu_nocb_leader_stride= [KNL]

			Set the number of NOCB kthread groups, which

			defaults to the square root of the number of

init/Kconfig

+12 −11
Original line number Diff line number Diff line
@@ -672,30 +672,31 @@ config RCU_BOOST 
	  Say Y here if you are working with real-time apps or heavy loads

	  Say N here if you are unsure.



config RCU_BOOST_PRIO

	int "Real-time priority to boost RCU readers to"

config RCU_KTHREAD_PRIO

	int "Real-time priority to use for RCU worker threads"

	range 1 99

	depends on RCU_BOOST

	default 1

	help

	  This option specifies the real-time priority to which long-term

	  preempted RCU readers are to be boosted.  If you are working

	  with a real-time application that has one or more CPU-bound

	  threads running at a real-time priority level, you should set

	  RCU_BOOST_PRIO to a priority higher then the highest-priority

	  real-time CPU-bound thread.  The default RCU_BOOST_PRIO value

	  of 1 is appropriate in the common case, which is real-time

	  This option specifies the SCHED_FIFO priority value that will be

	  assigned to the rcuc/n and rcub/n threads and is also the value

	  used for RCU_BOOST (if enabled). If you are working with a

	  real-time application that has one or more CPU-bound threads

	  running at a real-time priority level, you should set

	  RCU_KTHREAD_PRIO to a priority higher than the highest-priority

	  real-time CPU-bound application thread.  The default RCU_KTHREAD_PRIO

	  value of 1 is appropriate in the common case, which is real-time

	  applications that do not have any CPU-bound threads.



	  Some real-time applications might not have a single real-time

	  thread that saturates a given CPU, but instead might have

	  multiple real-time threads that, taken together, fully utilize

	  that CPU.  In this case, you should set RCU_BOOST_PRIO to

	  that CPU.  In this case, you should set RCU_KTHREAD_PRIO to

	  a priority higher than the lowest-priority thread that is

	  conspiring to prevent the CPU from running any non-real-time

	  tasks.  For example, if one thread at priority 10 and another

	  thread at priority 5 are between themselves fully consuming

	  the CPU time on a given CPU, then RCU_BOOST_PRIO should be

	  the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be

	  set to priority 6 or higher.



	  Specify the real-time priority, or take the default if unsure.

kernel/rcu/tree_plugin.h

+10 −10
Original line number Diff line number Diff line
@@ -30,12 +30,13 @@ 
#include <linux/smpboot.h>

#include "../time/tick-internal.h"



#define RCU_KTHREAD_PRIO 1



#ifdef CONFIG_RCU_BOOST



#include "../locking/rtmutex_common.h"

#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO



/* rcuc/rcub kthread realtime priority */

static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;

module_param(kthread_prio, int, 0644);



/*

 * Control variables for per-CPU and per-rcu_node kthreads.  These
@@ -46,11 +47,7 @@ DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); 
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);

DEFINE_PER_CPU(char, rcu_cpu_has_work);



#else /* #ifdef CONFIG_RCU_BOOST */



#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO



#endif /* #else #ifdef CONFIG_RCU_BOOST */

#endif /* #ifdef CONFIG_RCU_BOOST */



#ifdef CONFIG_RCU_NOCB_CPU

static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
@@ -98,6 +95,9 @@ static void __init rcu_bootup_announce_oddness(void) 
		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);

	if (nr_cpu_ids != NR_CPUS)

		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);

#ifdef CONFIG_RCU_BOOST

	pr_info("\tRCU kthread priority: %d.\n", kthread_prio);

#endif

}



#ifdef CONFIG_TREE_PREEMPT_RCU
@@ -1339,7 +1339,7 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, 
	smp_mb__after_unlock_lock();

	rnp->boost_kthread_task = t;

	raw_spin_unlock_irqrestore(&rnp->lock, flags);

	sp.sched_priority = RCU_BOOST_PRIO;

	sp.sched_priority = kthread_prio;

	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);

	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */

	return 0;
@@ -1356,7 +1356,7 @@ static void rcu_cpu_kthread_setup(unsigned int cpu) 
{

	struct sched_param sp;



	sp.sched_priority = RCU_KTHREAD_PRIO;

	sp.sched_priority = kthread_prio;

	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);

}

tools/testing/selftests/rcutorture/configs/rcu/TREE03

+1 −1
Original line number Diff line number Diff line
@@ -17,5 +17,5 @@ CONFIG_DEBUG_LOCK_ALLOC=n 
CONFIG_RCU_CPU_STALL_INFO=n

CONFIG_RCU_CPU_STALL_VERBOSE=n

CONFIG_RCU_BOOST=y

CONFIG_RCU_BOOST_PRIO=2

CONFIG_RCU_KTHREAD_PRIO=2

CONFIG_DEBUG_OBJECTS_RCU_HEAD=n

tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt

+2 −2
Original line number Diff line number Diff line
@@ -15,8 +15,8 @@ CONFIG_PREEMPT -- Do half. (First three and #8.) 
CONFIG_PROVE_LOCKING -- Do all but two, covering CONFIG_PROVE_RCU and not.

CONFIG_PROVE_RCU -- Do all but one under CONFIG_PROVE_LOCKING.

CONFIG_RCU_BOOST -- one of TREE_PREEMPT_RCU.

CONFIG_RCU_BOOST_PRIO -- set to 2 for _BOOST testing.

CONFIG_RCU_CPU_STALL_INFO -- do one with and without _VERBOSE.

CONFIG_RCU_KTHREAD_PRIO -- set to 2 for _BOOST testing.

CONFIG_RCU_CPU_STALL_INFO -- Do one.

CONFIG_RCU_CPU_STALL_VERBOSE -- do one with and without _INFO.

CONFIG_RCU_FANOUT -- Cover hierarchy as currently, but overlap with others.

CONFIG_RCU_FANOUT_EXACT -- Do one.