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authorJosé Pekkarinen <jose.pekkarinen@nokia.com>2016-05-18 13:18:31 +0300
committerJosé Pekkarinen <jose.pekkarinen@nokia.com>2016-05-18 13:42:15 +0300
commit437fd90c0250dee670290f9b714253671a990160 (patch)
treeb871786c360704244a07411c69fb58da9ead4a06 /qemu/util/qemu-thread-win32.c
parent5bbd6fe9b8bab2a93e548c5a53b032d1939eec05 (diff)
These changes are the raw update to qemu-2.6.
Collission happened in the following patches: migration: do cleanup operation after completion(738df5b9) Bug fix.(1750c932f86) kvmclock: add a new function to update env->tsc.(b52baab2) The code provided by the patches was already in the upstreamed version. Change-Id: I3cc11841a6a76ae20887b2e245710199e1ea7f9a Signed-off-by: José Pekkarinen <jose.pekkarinen@nokia.com>
Diffstat (limited to 'qemu/util/qemu-thread-win32.c')
-rw-r--r--qemu/util/qemu-thread-win32.c69
1 files changed, 63 insertions, 6 deletions
diff --git a/qemu/util/qemu-thread-win32.c b/qemu/util/qemu-thread-win32.c
index 406b52f91..98a5ddff8 100644
--- a/qemu/util/qemu-thread-win32.c
+++ b/qemu/util/qemu-thread-win32.c
@@ -10,12 +10,11 @@
* See the COPYING file in the top-level directory.
*
*/
+#include "qemu/osdep.h"
#include "qemu-common.h"
#include "qemu/thread.h"
#include "qemu/notify.h"
#include <process.h>
-#include <assert.h>
-#include <limits.h>
static bool name_threads;
@@ -238,10 +237,34 @@ void qemu_sem_wait(QemuSemaphore *sem)
}
}
+/* Wrap a Win32 manual-reset event with a fast userspace path. The idea
+ * is to reset the Win32 event lazily, as part of a test-reset-test-wait
+ * sequence. Such a sequence is, indeed, how QemuEvents are used by
+ * RCU and other subsystems!
+ *
+ * Valid transitions:
+ * - free->set, when setting the event
+ * - busy->set, when setting the event, followed by futex_wake
+ * - set->free, when resetting the event
+ * - free->busy, when waiting
+ *
+ * set->busy does not happen (it can be observed from the outside but
+ * it really is set->free->busy).
+ *
+ * busy->free provably cannot happen; to enforce it, the set->free transition
+ * is done with an OR, which becomes a no-op if the event has concurrently
+ * transitioned to free or busy (and is faster than cmpxchg).
+ */
+
+#define EV_SET 0
+#define EV_FREE 1
+#define EV_BUSY -1
+
void qemu_event_init(QemuEvent *ev, bool init)
{
/* Manual reset. */
- ev->event = CreateEvent(NULL, TRUE, init, NULL);
+ ev->event = CreateEvent(NULL, TRUE, TRUE, NULL);
+ ev->value = (init ? EV_SET : EV_FREE);
}
void qemu_event_destroy(QemuEvent *ev)
@@ -251,17 +274,51 @@ void qemu_event_destroy(QemuEvent *ev)
void qemu_event_set(QemuEvent *ev)
{
- SetEvent(ev->event);
+ if (atomic_mb_read(&ev->value) != EV_SET) {
+ if (atomic_xchg(&ev->value, EV_SET) == EV_BUSY) {
+ /* There were waiters, wake them up. */
+ SetEvent(ev->event);
+ }
+ }
}
void qemu_event_reset(QemuEvent *ev)
{
- ResetEvent(ev->event);
+ if (atomic_mb_read(&ev->value) == EV_SET) {
+ /* If there was a concurrent reset (or even reset+wait),
+ * do nothing. Otherwise change EV_SET->EV_FREE.
+ */
+ atomic_or(&ev->value, EV_FREE);
+ }
}
void qemu_event_wait(QemuEvent *ev)
{
- WaitForSingleObject(ev->event, INFINITE);
+ unsigned value;
+
+ value = atomic_mb_read(&ev->value);
+ if (value != EV_SET) {
+ if (value == EV_FREE) {
+ /* qemu_event_set is not yet going to call SetEvent, but we are
+ * going to do another check for EV_SET below when setting EV_BUSY.
+ * At that point it is safe to call WaitForSingleObject.
+ */
+ ResetEvent(ev->event);
+
+ /* Tell qemu_event_set that there are waiters. No need to retry
+ * because there cannot be a concurent busy->free transition.
+ * After the CAS, the event will be either set or busy.
+ */
+ if (atomic_cmpxchg(&ev->value, EV_FREE, EV_BUSY) == EV_SET) {
+ value = EV_SET;
+ } else {
+ value = EV_BUSY;
+ }
+ }
+ if (value == EV_BUSY) {
+ WaitForSingleObject(ev->event, INFINITE);
+ }
+ }
}
struct QemuThreadData {