[PATCH] lglock: Map to spinlock when !CONFIG_SMP

From: Josh Triplett
Date: Fri Oct 25 2013 - 11:19:47 EST

When the system has only one CPU, lglock is effectively a spinlock; map
it directly to spinlock to eliminate the indirection and duplicate code.

In addition to removing overhead, this drops 1.6k of code with a defconfig
modified to have !CONFIG_SMP, and 1.1k with a minimal config.

Signed-off-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
include/linux/lglock.h | 16 ++++++++++++++++
kernel/Makefile | 4 ++--
2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/include/linux/lglock.h b/include/linux/lglock.h
index 0d24e93..6561b1c 100644
--- a/include/linux/lglock.h
+++ b/include/linux/lglock.h
@@ -35,6 +35,8 @@

+#ifdef CONFIG_SMP
#define LOCKDEP_INIT_MAP lockdep_init_map
@@ -67,4 +69,18 @@ void lg_local_unlock_cpu(struct lglock *lg, int cpu);
void lg_global_lock(struct lglock *lg);
void lg_global_unlock(struct lglock *lg);

+/* When !CONFIG_SMP, map lglock to spinlock */
+#define lglock spinlock
+#define DEFINE_STATIC_LGLOCK(name) static DEFINE_SPINLOCK(name)
+#define lg_lock_init(lg, name) spin_lock_init(lg)
+#define lg_local_lock spin_lock
+#define lg_local_unlock spin_unlock
+#define lg_local_lock_cpu(lg, cpu) spin_lock(lg)
+#define lg_local_unlock_cpu(lg, cpu) spin_unlock(lg)
+#define lg_global_lock spin_lock
+#define lg_global_unlock spin_unlock
diff --git a/kernel/Makefile b/kernel/Makefile
index 1ce4755..84a89f7 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -10,7 +10,7 @@ obj-y = fork.o exec_domain.o panic.o \
kthread.o wait.o sys_ni.o posix-cpu-timers.o mutex.o \
hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
notifier.o ksysfs.o cred.o reboot.o \
- async.o range.o groups.o lglock.o smpboot.o
+ async.o range.o groups.o smpboot.o

# Do not trace debug files and internal ftrace files
@@ -50,7 +50,7 @@ obj-$(CONFIG_SMP) += smp.o
ifneq ($(CONFIG_SMP),y)
obj-y += up.o
-obj-$(CONFIG_SMP) += spinlock.o
+obj-$(CONFIG_SMP) += lglock.o spinlock.o
obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
obj-$(CONFIG_UID16) += uid16.o

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