From 64b47e8fdb40a0d46e8cf458dd3e24f8afa073f6 Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Mon, 7 Apr 2014 15:39:45 -0700
Subject: [PATCH] lglock: map to spinlock when !CONFIG_SMP

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@joshtriplett.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Howells <dhowells@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 include/linux/lglock.h  | 16 ++++++++++++++++
 kernel/locking/Makefile |  3 ++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/linux/lglock.h b/include/linux/lglock.h
index 96549abe8842..0081f000e34b 100644
--- a/include/linux/lglock.h
+++ b/include/linux/lglock.h
@@ -25,6 +25,8 @@
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 
+#ifdef CONFIG_SMP
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 #define LOCKDEP_INIT_MAP lockdep_init_map
 #else
@@ -57,4 +59,18 @@ void lg_local_unlock_cpu(struct lglock *lg, int cpu);
 void lg_global_lock(struct lglock *lg);
 void lg_global_unlock(struct lglock *lg);
 
+#else
+/* When !CONFIG_SMP, map lglock to spinlock */
+#define lglock spinlock
+#define DEFINE_LGLOCK(name) DEFINE_SPINLOCK(name)
+#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
+#endif
+
 #endif
diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile
index 306a76b51e0f..b8bdcd4785b7 100644
--- a/kernel/locking/Makefile
+++ b/kernel/locking/Makefile
@@ -1,5 +1,5 @@
 
-obj-y += mutex.o semaphore.o rwsem.o lglock.o mcs_spinlock.o
+obj-y += mutex.o semaphore.o rwsem.o mcs_spinlock.o
 
 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_lockdep.o = -pg
@@ -14,6 +14,7 @@ ifeq ($(CONFIG_PROC_FS),y)
 obj-$(CONFIG_LOCKDEP) += lockdep_proc.o
 endif
 obj-$(CONFIG_SMP) += spinlock.o
+obj-$(CONFIG_SMP) += lglock.o
 obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
 obj-$(CONFIG_RT_MUTEXES) += rtmutex.o
 obj-$(CONFIG_DEBUG_RT_MUTEXES) += rtmutex-debug.o
-- 
2.11.0