[PATCH tip/core/rcu 03/12] rcu: Distinguish "rcuo" kthreads by RCU flavor
From: "Paul E. McKenney"
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 use used
to distinguish the "rcuo" kthreads, for example, for CPU 0 we would have
"rcuo0b", "rcuo0p", and "rcuo0s".
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 6c72381..c2c3abf 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2432,9 +2432,12 @@ 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 9a04156..82f4e3c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -676,12 +676,13 @@ 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 433f426..074cb2d 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 = { ##_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 e51373c..b6c2335 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
[PATCH tip/core/rcu 03/12] rcu: Distinguish rcuo kthreads by RCU flavor
From: Paul E. McKenney paul.mcken...@linaro.org
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 use used
to distinguish the rcuo kthreads, for example, for CPU 0 we would have
rcuo0b, rcuo0p, and rcuo0s.
Signed-off-by: Paul E. McKenney paul.mcken...@linaro.org
Signed-off-by: Paul E. McKenney paul...@linux.vnet.ibm.com
Tested-by: Dietmar Eggemann dietmar.eggem...@arm.com
---
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 6c72381..c2c3abf 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2432,9 +2432,12 @@ 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 9a04156..82f4e3c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -676,12 +676,13 @@ 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 433f426..074cb2d 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 e51373c..b6c2335 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. */
