Re: [PATCH v6 04/46] percpu_rwlock: Implement the core design of Per-CPU Reader-Writer Locks
From: Lai Jiangshan <hidden>
Date: 2013-02-25 15:53:28
Also in:
linux-arch, linux-arm-kernel, linux-pm, lkml, netdev
Subsystem:
the rest · Maintainer:
Linus Torvalds
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 <redacted> 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 <redacted> --- 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);
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1.7.7.6