[PATCH v7 08/13] multifd: Prepare to send a packet without the mutex held

[Juan Quintela]

We do the send_prepare() and the fill of the head packet without the
mutex held.  It will help a lot for compression and later in the
series for zero pages.

Notice that we can use p->pages without holding p->mutex because
p->pending_job == 1.

Signed-off-by: Juan Quintela <quint...@redhat.com>
---
 migration/multifd.h |  2 ++
 migration/multifd.c | 11 ++++++-----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/migration/multifd.h b/migration/multifd.h
index af8ce8921d..d48597a1ea 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -109,7 +109,9 @@ typedef struct {
     /* array of pages to sent.
      * The owner of 'pages' depends of 'pending_job' value:
      * pending_job == 0 -> migration_thread can use it.
+     *                     No need for mutex lock.
      * pending_job != 0 -> multifd_channel can use it.
+     *                     No need for mutex lock.
      */
     MultiFDPages_t *pages;
 
diff --git a/migration/multifd.c b/migration/multifd.c
index 69b9d7cf98..056599cbaf 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -661,6 +661,8 @@ static void *multifd_send_thread(void *opaque)
                 p->flags |= MULTIFD_FLAG_SYNC;
                 p->sync_needed = false;
             }
+            qemu_mutex_unlock(&p->mutex);
+
             p->normal_num = 0;
 
             if (use_zero_copy_send) {
@@ -682,11 +684,6 @@ static void *multifd_send_thread(void *opaque)
                 }
             }
             multifd_send_fill_packet(p);
-            p->num_packets++;
-            p->total_normal_pages += p->normal_num;
-            p->pages->num = 0;
-            p->pages->block = NULL;
-            qemu_mutex_unlock(&p->mutex);
 
             trace_multifd_send(p->id, packet_num, p->normal_num, p->flags,
                                p->next_packet_size);
@@ -711,6 +708,10 @@ static void *multifd_send_thread(void *opaque)
             }
 
             qemu_mutex_lock(&p->mutex);
+            p->num_packets++;
+            p->total_normal_pages += p->normal_num;
+            p->pages->num = 0;
+            p->pages->block = NULL;
             p->sent_bytes += p->packet_len;;
             p->sent_bytes += p->next_packet_size;
             p->pending_job--;
-- 
2.35.3