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 <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4609e81dbc37fc2dbfa005ff607890df3a8bbc6b..a17ba16c8fc8e3977760d614833a0e24636c2aa5 100644 (file)
--- 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 30749970458081bbc943f7b46cdb27d23cb83d6c..717584064a7ea7e67df219de16172f9196e746cc 100644 (file)
--- 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 433f426c848f92fa6e93666c89692f7807b78ee1..074cb2d974bfc0ff39b5a9fdadc9266203f6c07a 100644 (file)
--- 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 e51373c0b74840edf4380b47ca44840a2ad0dfc9..b6c2335efbdf54fbc73bd61910ffc46eb8490eb8 100644 (file)
--- 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 e32236e83dda374f2c72d655db89dbde5d51b91d..c0164441ab922d7707db3e5423efad01a4dfe16f 100644 (file)
--- 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;
        }