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: Clark Williams <clark.williams@gmail.com> [ paulmck: Ported to rcu/dev, applied Paul Bolle and Peter Zijlstra feedback. ] Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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@ -2922,6 +2922,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
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quiescent states. Units are jiffies, minimum
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value is one, and maximum value is HZ.
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rcutree.kthread_prio= [KNL,BOOT]
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Set the SCHED_FIFO priority of the RCU
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per-CPU kthreads (rcuc/N). This value is also
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used for the priority of the RCU boost threads
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(rcub/N). Valid values are 1-99 and the default
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is 1 (the least-favored priority).
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rcutree.rcu_nocb_leader_stride= [KNL]
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Set the number of NOCB kthread groups, which
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defaults to the square root of the number of
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23
init/Kconfig
23
init/Kconfig
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@ -672,30 +672,31 @@ config RCU_BOOST
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Say Y here if you are working with real-time apps or heavy loads
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Say N here if you are unsure.
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config RCU_BOOST_PRIO
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int "Real-time priority to boost RCU readers to"
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config RCU_KTHREAD_PRIO
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int "Real-time priority to use for RCU worker threads"
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range 1 99
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depends on RCU_BOOST
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default 1
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help
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This option specifies the real-time priority to which long-term
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preempted RCU readers are to be boosted. If you are working
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with a real-time application that has one or more CPU-bound
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threads running at a real-time priority level, you should set
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RCU_BOOST_PRIO to a priority higher then the highest-priority
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real-time CPU-bound thread. The default RCU_BOOST_PRIO value
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of 1 is appropriate in the common case, which is real-time
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This option specifies the SCHED_FIFO priority value that will be
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assigned to the rcuc/n and rcub/n threads and is also the value
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used for RCU_BOOST (if enabled). If you are working with a
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real-time application that has one or more CPU-bound threads
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running at a real-time priority level, you should set
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RCU_KTHREAD_PRIO to a priority higher than the highest-priority
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real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
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value of 1 is appropriate in the common case, which is real-time
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applications that do not have any CPU-bound threads.
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Some real-time applications might not have a single real-time
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thread that saturates a given CPU, but instead might have
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multiple real-time threads that, taken together, fully utilize
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that CPU. In this case, you should set RCU_BOOST_PRIO to
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that CPU. In this case, you should set RCU_KTHREAD_PRIO to
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a priority higher than the lowest-priority thread that is
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conspiring to prevent the CPU from running any non-real-time
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tasks. For example, if one thread at priority 10 and another
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thread at priority 5 are between themselves fully consuming
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the CPU time on a given CPU, then RCU_BOOST_PRIO should be
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the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
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set to priority 6 or higher.
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Specify the real-time priority, or take the default if unsure.
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@ -30,12 +30,13 @@
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#include <linux/smpboot.h>
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#include "../time/tick-internal.h"
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#define RCU_KTHREAD_PRIO 1
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#ifdef CONFIG_RCU_BOOST
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#include "../locking/rtmutex_common.h"
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#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
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/* rcuc/rcub kthread realtime priority */
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static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
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module_param(kthread_prio, int, 0644);
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/*
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* Control variables for per-CPU and per-rcu_node kthreads. These
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@ -46,11 +47,7 @@ DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
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DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
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DEFINE_PER_CPU(char, rcu_cpu_has_work);
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#else /* #ifdef CONFIG_RCU_BOOST */
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#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
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#endif /* #else #ifdef CONFIG_RCU_BOOST */
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#endif /* #ifdef CONFIG_RCU_BOOST */
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#ifdef CONFIG_RCU_NOCB_CPU
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static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
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@ -98,6 +95,9 @@ static void __init rcu_bootup_announce_oddness(void)
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pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
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if (nr_cpu_ids != NR_CPUS)
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pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
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#ifdef CONFIG_RCU_BOOST
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pr_info("\tRCU kthread priority: %d.\n", kthread_prio);
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#endif
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}
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#ifdef CONFIG_TREE_PREEMPT_RCU
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@ -1339,7 +1339,7 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
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smp_mb__after_unlock_lock();
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rnp->boost_kthread_task = t;
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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sp.sched_priority = RCU_BOOST_PRIO;
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sp.sched_priority = kthread_prio;
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sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
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return 0;
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@ -1356,7 +1356,7 @@ static void rcu_cpu_kthread_setup(unsigned int cpu)
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{
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struct sched_param sp;
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sp.sched_priority = RCU_KTHREAD_PRIO;
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sp.sched_priority = kthread_prio;
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sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
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}
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@ -17,5 +17,5 @@ CONFIG_DEBUG_LOCK_ALLOC=n
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CONFIG_RCU_CPU_STALL_INFO=n
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CONFIG_RCU_CPU_STALL_VERBOSE=n
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CONFIG_RCU_BOOST=y
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CONFIG_RCU_BOOST_PRIO=2
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CONFIG_RCU_KTHREAD_PRIO=2
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CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
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@ -15,8 +15,8 @@ CONFIG_PREEMPT -- Do half. (First three and #8.)
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CONFIG_PROVE_LOCKING -- Do all but two, covering CONFIG_PROVE_RCU and not.
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CONFIG_PROVE_RCU -- Do all but one under CONFIG_PROVE_LOCKING.
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CONFIG_RCU_BOOST -- one of TREE_PREEMPT_RCU.
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CONFIG_RCU_BOOST_PRIO -- set to 2 for _BOOST testing.
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CONFIG_RCU_CPU_STALL_INFO -- do one with and without _VERBOSE.
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CONFIG_RCU_KTHREAD_PRIO -- set to 2 for _BOOST testing.
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CONFIG_RCU_CPU_STALL_INFO -- Do one.
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CONFIG_RCU_CPU_STALL_VERBOSE -- do one with and without _INFO.
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CONFIG_RCU_FANOUT -- Cover hierarchy as currently, but overlap with others.
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CONFIG_RCU_FANOUT_EXACT -- Do one.
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