rcu: Unify boost and kthread priorities (21871d7e) · Commits · 戴 / test

Documentation/kernel-parameters.txt

+7 −0

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		@@ -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

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		@@ -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

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		@@ -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

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		@@ -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.

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