migration: hold the lock only if it is really needed
Try to hold src_page_req_mutex only if the queue is not
empty
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/include/qemu/queue.h b/include/qemu/queue.h
index 59fd120..ac418ef 100644
--- a/include/qemu/queue.h
+++ b/include/qemu/queue.h
@@ -341,6 +341,7 @@
/*
* Simple queue access methods.
*/
+#define QSIMPLEQ_EMPTY_ATOMIC(head) (atomic_read(&((head)->sqh_first)) == NULL)
#define QSIMPLEQ_EMPTY(head) ((head)->sqh_first == NULL)
#define QSIMPLEQ_FIRST(head) ((head)->sqh_first)
#define QSIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next)
diff --git a/migration/ram.c b/migration/ram.c
index 40013e6..79c8942 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2033,6 +2033,10 @@
{
RAMBlock *block = NULL;
+ if (QSIMPLEQ_EMPTY_ATOMIC(&rs->src_page_requests)) {
+ return NULL;
+ }
+
qemu_mutex_lock(&rs->src_page_req_mutex);
if (!QSIMPLEQ_EMPTY(&rs->src_page_requests)) {
struct RAMSrcPageRequest *entry =
