From ce4cdd45c87a89af71128e6bf676ba5a60ad0314 Mon Sep 17 00:00:00 2001 From: Samy Al Bahra Date: Sun, 19 Aug 2012 16:20:17 -0400 Subject: [PATCH] ck_spinlock: Adopt RMO semantics for CLH. --- include/ck_spinlock.h | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/include/ck_spinlock.h b/include/ck_spinlock.h index 080b3bf..eca0d2c 100644 --- a/include/ck_spinlock.h +++ b/include/ck_spinlock.h @@ -586,7 +586,7 @@ ck_spinlock_mcs_unlock(struct ck_spinlock_mcs **queue, struct ck_spinlock_mcs *n struct ck_spinlock_clh { unsigned int wait; - struct ck_spinlock_clh_thread *previous; + struct ck_spinlock_clh *previous; }; typedef struct ck_spinlock_clh ck_spinlock_clh_t; @@ -606,13 +606,16 @@ ck_spinlock_clh_lock(struct ck_spinlock_clh **queue, struct ck_spinlock_clh *thr { struct ck_spinlock_clh *previous; + /* Indicate to the next thread on queue that they will have to block. */ ck_pr_store_uint(&thread->wait, true); + ck_pr_fence_store(); /* Mark current request as last request. Save reference to previous request. */ previous = ck_pr_fas_ptr(queue, thread); - ck_pr_store_ptr(&thread->previous, previous); + thread->previous = previous; /* Wait until previous thread is done with lock. */ + ck_pr_fence_load(); while (ck_pr_load_uint(&previous->wait) == true) ck_pr_stall(); @@ -624,8 +627,6 @@ ck_spinlock_clh_unlock(struct ck_spinlock_clh **thread) { struct ck_spinlock_clh *previous; - ck_pr_fence_memory(); - /* * If there are waiters, they are spinning on the current node wait * flag. The flag is cleared so that the successor may complete an @@ -633,7 +634,10 @@ ck_spinlock_clh_unlock(struct ck_spinlock_clh **thread) * may be updated by a successor's lock operation. In order to avoid * this, save a copy of the predecessor before setting the flag. */ - previous = ck_pr_load_ptr(&(*thread)->previous); + previous = thread[0]->previous; + + /* We have to pay this cost anyways, use it as a compiler barrier too. */ + ck_pr_fence_memory(); ck_pr_store_uint(&(*thread)->wait, false); /* @@ -641,7 +645,7 @@ ck_spinlock_clh_unlock(struct ck_spinlock_clh **thread) * so update caller to use previous structure. This allows successor * all the time in the world to successfully read updated wait flag. */ - ck_pr_store_ptr(thread, previous); + *thread = previous; return; } #endif /* CK_F_SPINLOCK_CLH */