From ae526e32bd36cfb84045c8d2fd34e0b9e39a52f8 Mon Sep 17 00:00:00 2001
From: Xiao Guangrong
Date: Tue, 21 Aug 2018 16:10:25 +0800
Subject: 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>
---
 migration/ram.c | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'migration')

diff --git a/migration/ram.c b/migration/ram.c
index 40013e68a1..79c89425a3 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2033,6 +2033,10 @@ static RAMBlock *unqueue_page(RAMState *rs, ram_addr_t *offset)
 {
     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 =
-- 
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