Hi, Srivatsa,
The target of the whole patchset is nice for me.
A question: How did you find out the such usages of
"preempt_disable()" and convert them? did all are converted?
And I think the lock is too complex and reinvent the wheel, why don't
you reuse the lglock?
I wrote an untested draft here.
Thanks,
Lai
PS: Some HA tools(I'm writing one) which takes checkpoints of
virtual-machines frequently, I guess this patchset can speedup the
tools.
>From 01db542693a1b7fc6f9ece45d57cb529d9be5b66 Mon Sep 17 00:00:00 2001
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Date: Mon, 25 Feb 2013 23:14:27 +0800
Subject: [PATCH] lglock: add read-preference local-global rwlock
locality via lglock(trylock)
read-preference read-write-lock via fallback rwlock_t
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
include/linux/lglock.h | 31 +++++++++++++++++++++++++++++++
kernel/lglock.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 76 insertions(+), 0 deletions(-)
diff --git a/include/linux/lglock.h b/include/linux/lglock.h
index 0d24e93..30fe887 100644
--- a/include/linux/lglock.h
+++ b/include/linux/lglock.h
@@ -67,4 +67,35 @@ void lg_local_unlock_cpu(struct lglock *lg, int cpu);
void lg_global_lock(struct lglock *lg);
void lg_global_unlock(struct lglock *lg);
+struct lgrwlock {
+ unsigned long __percpu *fallback_reader_refcnt;
+ struct lglock lglock;
+ rwlock_t fallback_rwlock;
+};
+
+#define DEFINE_LGRWLOCK(name) \
+ static DEFINE_PER_CPU(arch_spinlock_t, name ## _lock) \
+ = __ARCH_SPIN_LOCK_UNLOCKED; \
+ static DEFINE_PER_CPU(unsigned long, name ## _refcnt); \
+ struct lgrwlock name = { \
+ .fallback_reader_refcnt = &name ## _refcnt, \
+ .lglock = { .lock = &name ## _lock } }
+
+#define DEFINE_STATIC_LGRWLOCK(name) \
+ static DEFINE_PER_CPU(arch_spinlock_t, name ## _lock) \
+ = __ARCH_SPIN_LOCK_UNLOCKED; \
+ static DEFINE_PER_CPU(unsigned long, name ## _refcnt); \
+ static struct lgrwlock name = { \
+ .fallback_reader_refcnt = &name ## _refcnt, \
+ .lglock = { .lock = &name ## _lock } }
+
+static inline void lg_rwlock_init(struct lgrwlock *lgrw, char *name)
+{
+ lg_lock_init(&lgrw->lglock, name);
+}
+
+void lg_rwlock_local_read_lock(struct lgrwlock *lgrw);
+void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw);
+void lg_rwlock_global_write_lock(struct lgrwlock *lgrw);
+void lg_rwlock_global_write_unlock(struct lgrwlock *lgrw);
#endif
diff --git a/kernel/lglock.c b/kernel/lglock.c
index 6535a66..463543a 100644
--- a/kernel/lglock.c
+++ b/kernel/lglock.c
@@ -87,3 +87,48 @@ void lg_global_unlock(struct lglock *lg)
preempt_enable();
}
EXPORT_SYMBOL(lg_global_unlock);
+
+void lg_rwlock_local_read_lock(struct lgrwlock *lgrw)
+{
+ struct lglock *lg = &lgrw->lglock;
+
+ preempt_disable();
+ if (likely(!__this_cpu_read(*lgrw->fallback_reader_refcnt))) {
+ if (likely(arch_spin_trylock(this_cpu_ptr(lg->lock)))) {
+ rwlock_acquire_read(&lg->lock_dep_map, 0, 0, _RET_IP_);
+ return;
+ }
+ read_lock(&lgrw->fallback_rwlock);
+ }
+
+ __this_cpu_inc(*lgrw->fallback_reader_refcnt);
+}
+EXPORT_SYMBOL(lg_rwlock_local_read_lock);
+
+void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw)
+{
+ if (likely(!__this_cpu_read(*lgrw->fallback_reader_refcnt))) {
+ lg_local_unlock(&lgrw->lglock);
+ return;
+ }
+
+ if (!__this_cpu_dec_return(*lgrw->fallback_reader_refcnt))
+ read_unlock(&lgrw->fallback_rwlock);
+
+ preempt_enable();
+}
+EXPORT_SYMBOL(lg_rwlock_local_read_unlock);
+
+void lg_rwlock_global_write_lock(struct lgrwlock *lgrw)
+{
+ lg_global_lock(&lgrw->lglock);
+ write_lock(&lgrw->fallback_rwlock);
+}
+EXPORT_SYMBOL(lg_rwlock_global_write_lock);
+
+void lg_rwlock_global_write_unlock(struct lgrwlock *lgrw)
+{
+ write_unlock(&lgrw->fallback_rwlock);
+ lg_global_unlock(&lgrw->lglock);
+}
+EXPORT_SYMBOL(lg_rwlock_global_write_unlock);
--
1.7.7.6
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