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Commit a4889858 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
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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: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
parent 09c7b890

Documentation/kernel-parameters.txt

+5 −2
Original line number Diff line number Diff line
@@ -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.

init/Kconfig

+7 −6
Original line number Diff line number Diff line
@@ -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.

kernel/rcutree.c

+4 −3
Original line number Diff line number Diff line
@@ -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;

kernel/rcutree.h

+1 −0
Original line number Diff line number Diff line
@@ -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. */

};

kernel/rcutree_plugin.h

+3 −2
Original line number Diff line number Diff line
@@ -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;

	}