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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>
This commit is contained in:
Xiao Guangrong 2018-08-21 16:10:25 +08:00 committed by Juan Quintela
parent 5e5fdcff28
commit ae526e32bd
2 changed files with 5 additions and 0 deletions
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1
include/qemu/queue.h
View File

@ -341,6 +341,7 @@ struct { \
/* /*
* Simple queue access methods. * 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_EMPTY(head) ((head)->sqh_first == NULL)
#define QSIMPLEQ_FIRST(head) ((head)->sqh_first) #define QSIMPLEQ_FIRST(head) ((head)->sqh_first)
#define QSIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next) #define QSIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next)

4
migration/ram.c
View File

@ -2033,6 +2033,10 @@ static RAMBlock *unqueue_page(RAMState *rs, ram_addr_t *offset)
{ {
RAMBlock *block = NULL; RAMBlock *block = NULL;
if (QSIMPLEQ_EMPTY_ATOMIC(&rs->src_page_requests)) {
return NULL;
}
qemu_mutex_lock(&rs->src_page_req_mutex); qemu_mutex_lock(&rs->src_page_req_mutex);
if (!QSIMPLEQ_EMPTY(&rs->src_page_requests)) { if (!QSIMPLEQ_EMPTY(&rs->src_page_requests)) {
struct RAMSrcPageRequest *entry = struct RAMSrcPageRequest *entry =