From a488985851cf2facd2227bd982cc2c251df56268 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 3 Dec 2012 08:16:28 -0800 Subject: [PATCH] rcu: Distinguish "rcuo" kthreads by RCU flavor Currently, the per-no-CBs-CPU kthreads are named "rcuo" followed by the CPU number, for example, "rcuo". This is problematic given that there are either two or three RCU flavors, each of which gets a per-CPU kthread with exactly the same name. This commit therefore introduces a one-letter abbreviation for each RCU flavor, namely 'b' for RCU-bh, 'p' for RCU-preempt, and 's' for RCU-sched. This abbreviation is used to distinguish the "rcuo" kthreads, for example, for CPU 0 we would have "rcuob/0", "rcuop/0", and "rcuos/0". Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Dietmar Eggemann --- Documentation/kernel-parameters.txt | 7 +++++-- init/Kconfig | 13 +++++++------ kernel/rcutree.c | 7 ++++--- kernel/rcutree.h | 1 + kernel/rcutree_plugin.h | 5 +++-- 5 files changed, 20 insertions(+), 13 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 4609e81dbc37..a17ba16c8fc8 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2461,9 +2461,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. In kernels built with CONFIG_RCU_NOCB_CPU=y, set the specified list of CPUs to be no-callback CPUs. Invocation of these CPUs' RCU callbacks will - be offloaded to "rcuoN" kthreads created for - that purpose. This reduces OS jitter on the + be offloaded to "rcuox/N" kthreads created for + that purpose, where "x" is "b" for RCU-bh, "p" + for RCU-preempt, and "s" for RCU-sched, and "N" + is the CPU number. This reduces OS jitter on the offloaded CPUs, which can be useful for HPC and + real-time workloads. It can also improve energy efficiency for asymmetric multiprocessors. diff --git a/init/Kconfig b/init/Kconfig index 307499704580..717584064a7e 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -666,12 +666,13 @@ config RCU_NOCB_CPU This option offloads callback invocation from the set of CPUs specified at boot time by the rcu_nocbs parameter. - For each such CPU, a kthread ("rcuoN") will be created to - invoke callbacks, where the "N" is the CPU being offloaded. - Nothing prevents this kthread from running on the specified - CPUs, but (1) the kthreads may be preempted between each - callback, and (2) affinity or cgroups can be used to force - the kthreads to run on whatever set of CPUs is desired. + For each such CPU, a kthread ("rcuox/N") will be created to + invoke callbacks, where the "N" is the CPU being offloaded, + and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and + "s" for RCU-sched. Nothing prevents this kthread from running + on the specified CPUs, but (1) the kthreads may be preempted + between each callback, and (2) affinity or cgroups can be used + to force the kthreads to run on whatever set of CPUs is desired. Say Y here if you want to help to debug reduced OS jitter. Say N here if you are unsure. diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 433f426c848f..074cb2d974bf 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -64,7 +64,7 @@ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS]; static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS]; -#define RCU_STATE_INITIALIZER(sname, cr) { \ +#define RCU_STATE_INITIALIZER(sname, sabbr, cr) { \ .level = { &sname##_state.node[0] }, \ .call = cr, \ .fqs_state = RCU_GP_IDLE, \ @@ -76,13 +76,14 @@ static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS]; .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \ .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \ .name = #sname, \ + .abbr = sabbr, \ } struct rcu_state rcu_sched_state = - RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched); + RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched); DEFINE_PER_CPU(struct rcu_data, rcu_sched_data); -struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh, call_rcu_bh); +struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh); DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); static struct rcu_state *rcu_state; diff --git a/kernel/rcutree.h b/kernel/rcutree.h index e51373c0b748..b6c2335efbdf 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -443,6 +443,7 @@ struct rcu_state { unsigned long gp_max; /* Maximum GP duration in */ /* jiffies. */ char *name; /* Name of structure. */ + char abbr; /* Abbreviated name. */ struct list_head flavors; /* List of RCU flavors. */ }; diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index e32236e83dda..c0164441ab92 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -111,7 +111,7 @@ static void __init rcu_bootup_announce_oddness(void) #ifdef CONFIG_TREE_PREEMPT_RCU struct rcu_state rcu_preempt_state = - RCU_STATE_INITIALIZER(rcu_preempt, call_rcu); + RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); static struct rcu_state *rcu_state = &rcu_preempt_state; @@ -2517,7 +2517,8 @@ static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) return; for_each_cpu(cpu, rcu_nocb_mask) { rdp = per_cpu_ptr(rsp->rda, cpu); - t = kthread_run(rcu_nocb_kthread, rdp, "rcuo%d", cpu); + t = kthread_run(rcu_nocb_kthread, rdp, + "rcuo%c/%d", rsp->abbr, cpu); BUG_ON(IS_ERR(t)); ACCESS_ONCE(rdp->nocb_kthread) = t; }