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[Qemu-devel] [PATCH 3/4] membarrier: introduce qemu/sys_membarrier.h
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 3/4] membarrier: introduce qemu/sys_membarrier.h |
Date: |
Fri, 9 Mar 2018 14:29:21 +0100 |
This new header file provides heavy-weight "global" memory barriers that
enforce memory ordering on each running thread belonging to the current
process. For now, use a dummy implementation that issues memory barriers
on both sides (matching what QEMU has been doing so far).
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/rcu.h | 7 ++++---
include/qemu/sys_membarrier.h | 17 +++++++++++++++++
util/rcu.c | 9 +++++----
3 files changed, 26 insertions(+), 7 deletions(-)
create mode 100644 include/qemu/sys_membarrier.h
diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
index 625f09ac09..22876d1428 100644
--- a/include/qemu/rcu.h
+++ b/include/qemu/rcu.h
@@ -27,6 +27,7 @@
#include "qemu/thread.h"
#include "qemu/queue.h"
#include "qemu/atomic.h"
+#include "qemu/sys_membarrier.h"
#ifdef __cplusplus
extern "C" {
@@ -82,7 +83,7 @@ static inline void rcu_read_lock(void)
atomic_set(&p_rcu_reader->ctr, ctr);
/* Write p_rcu_reader->ctr before reading RCU-protected pointers. */
- smp_mb();
+ smp_mb_placeholder();
}
static inline void rcu_read_unlock(void)
@@ -96,13 +97,13 @@ static inline void rcu_read_unlock(void)
/* Ensure that the critical section is seen to precede the
* store to p_rcu_reader->ctr. Together with the following
- * smp_mb(), this ensures writes to p_rcu_reader->ctr
+ * smp_mb_placeholder(), this ensures writes to p_rcu_reader->ctr
* are sequentially consistent.
*/
atomic_store_release(&p_rcu_reader->ctr, 0);
/* Write p_rcu_reader->ctr before reading p_rcu_reader->waiting. */
- smp_mb();
+ smp_mb_placeholder();
if (unlikely(atomic_read(&p_rcu_reader->waiting))) {
atomic_set(&p_rcu_reader->waiting, false);
qemu_event_set(&rcu_gp_event);
diff --git a/include/qemu/sys_membarrier.h b/include/qemu/sys_membarrier.h
new file mode 100644
index 0000000000..9ce7f5210b
--- /dev/null
+++ b/include/qemu/sys_membarrier.h
@@ -0,0 +1,17 @@
+/*
+ * Process-global memory barriers
+ *
+ * Copyright (c) 2018 Red Hat, Inc.
+ *
+ * Author: Paolo Bonzini <address@hidden>
+ */
+
+#ifndef QEMU_SYS_MEMBARRIER_H
+#define QEMU_SYS_MEMBARRIER_H 1
+
+/* Keep it simple, execute a real memory barrier on both sides. */
+static inline void smp_mb_global_init(void) {}
+#define smp_mb_global() smp_mb()
+#define smp_mb_placeholder() smp_mb()
+
+#endif
diff --git a/util/rcu.c b/util/rcu.c
index 7366dc50dd..5676c22bd1 100644
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -93,10 +93,10 @@ static void wait_for_readers(void)
}
/* Here, order the stores to index->waiting before the loads of
- * index->ctr. Pairs with smp_mb() in rcu_read_unlock(),
+ * index->ctr. Pairs with smp_mb_placeholder() in rcu_read_unlock(),
* ensuring that the loads of index->ctr are sequentially consistent.
*/
- smp_mb();
+ smp_mb_global();
QLIST_FOREACH_SAFE(index, ®istry, node, tmp) {
if (!rcu_gp_ongoing(&index->ctr)) {
@@ -145,9 +145,9 @@ void synchronize_rcu(void)
qemu_mutex_lock(&rcu_sync_lock);
/* Write RCU-protected pointers before reading p_rcu_reader->ctr.
- * Pairs with smp_mb() in rcu_read_lock().
+ * Pairs with smp_mb_placeholder() in rcu_read_lock().
*/
- smp_mb();
+ smp_mb_global();
qemu_mutex_lock(&rcu_registry_lock);
if (!QLIST_EMPTY(®istry)) {
@@ -376,6 +376,7 @@ static void rcu_init_child(void)
static void __attribute__((__constructor__)) rcu_init(void)
{
+ smp_mb_global_init();
#ifdef CONFIG_POSIX
pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_child);
#endif
--
2.14.3
- [Qemu-devel] [PATCH 0/4] Optionally use membarrier system call for RCU, Paolo Bonzini, 2018/03/09
- [Qemu-devel] [PATCH 4/4] membarrier: add --enable-membarrier, Paolo Bonzini, 2018/03/09
- [Qemu-devel] [PATCH 2/4] rcu: make memory barriers more explicit, Paolo Bonzini, 2018/03/09
- [Qemu-devel] [PATCH 3/4] membarrier: introduce qemu/sys_membarrier.h,
Paolo Bonzini <=
- [Qemu-devel] [PATCH 1/4] rcutorture: remove synchronize_rcu from readers, Paolo Bonzini, 2018/03/09
- Re: [Qemu-devel] [PATCH 0/4] Optionally use membarrier system call for RCU, no-reply, 2018/03/09
- Re: [Qemu-devel] [PATCH 0/4] Optionally use membarrier system call for RCU, Emilio G. Cota, 2018/03/21