From 21871d7eff2c96ae67e18e00adf59d56940e2fcc Mon Sep 17 00:00:00 2001 From: Clark Williams Date: Fri, 12 Sep 2014 21:21:09 -0500 Subject: [PATCH] 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 [ paulmck: Ported to rcu/dev, applied Paul Bolle and Peter Zijlstra feedback. ] Signed-off-by: Paul E. McKenney --- Documentation/kernel-parameters.txt | 7 ++++++ init/Kconfig | 23 ++++++++++--------- kernel/rcu/tree_plugin.h | 20 ++++++++-------- .../selftests/rcutorture/configs/rcu/TREE03 | 2 +- .../rcutorture/doc/TREE_RCU-kconfig.txt | 4 ++-- 5 files changed, 32 insertions(+), 24 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 7dbe5ec9d9cd..6608520e9fa2 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -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 diff --git a/init/Kconfig b/init/Kconfig index 0c9546ba56e8..15c299cc7c1e 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -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. diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 357891104ea0..344f0e661515 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -30,12 +30,13 @@ #include #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); } diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE03 b/tools/testing/selftests/rcutorture/configs/rcu/TREE03 index f4567fb3e332..b95f62efd6f2 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE03 +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE03 @@ -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 diff --git a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt index 3e588db86a17..ab6e7b4103ac 100644 --- a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt +++ b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt @@ -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. -- 2.20.1