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[Qemu-devel] [PULL 25/69] membarrier: introduce qemu/sys_membarrier.h
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 25/69] membarrier: introduce qemu/sys_membarrier.h |
Date: |
Tue, 13 Mar 2018 23:46:35 +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] [PULL 14/69] chardev: introduce chr_machine_done hook, (continued)
- [Qemu-devel] [PULL 14/69] chardev: introduce chr_machine_done hook, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 16/69] chardev: tcp: postpone async connection setup, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 19/69] hw/i386: make IOMMUs configurable via default-configs/, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 18/69] scsi: support NDOB (no data-out buffer) for WRITE SAME commands, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 22/69] rcutorture: remove synchronize_rcu from readers, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 21/69] hw/mips/jazz: Fix implicit creation of "-drive if=scsi" devices, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 17/69] chardev: tcp: let TLS run on chardev context, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 20/69] Polish the version strings containing the package version, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 24/69] rcu: make memory barriers more explicit, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 23/69] docs: document atomic_load_acquire and atomic_store_release, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 25/69] membarrier: introduce qemu/sys_membarrier.h,
Paolo Bonzini <=
- [Qemu-devel] [PULL 26/69] membarrier: add --enable-membarrier, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 28/69] hw/dma/i8257: Rename DMA_init() to i8257_dma_init(), Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 27/69] hw/isa: Move parallel_hds_isa_init() to hw/char/parallel-isa.c, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 30/69] MAINTAINERS: Fix the PC87312 include path, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 29/69] hw/input/i8042: Extract declarations from i386/pc.h into input/i8042.h, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 31/69] hw/isa/pc87312: Rename the device type as TYPE_PC87312_SUPERIO, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 32/69] hw/isa/pc87312: Use uint16_t for the ISA I/O base address, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 33/69] hw/isa/pc87312: Use 'unsigned int' for the irq value, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 34/69] hw/isa/superio: Add a Super I/O template based on the PC87312 device, Paolo Bonzini, 2018/03/13
- [Qemu-devel] [PULL 36/69] hw/isa/superio: Factor out the parallel code from pc87312.c, Paolo Bonzini, 2018/03/13