[Qemu-devel] [PATCH 2/2] vhost-user: only seek a reply if needed in set_mem_table

[Maxime Coquelin]

The goal of this patch is to only request a sync (reply_ack,
or get_features) in set_mem_table only when necessary.

It should not be necessary the first time we set the table,
or when we add a new regions which hadn't been merged with an
existing ones.

Suggested-by: Michael S. Tsirkin <address@hidden>
Cc: Prerna Saxena <address@hidden>
Cc: Marc-André Lureau <address@hidden>
Signed-off-by: Maxime Coquelin <address@hidden>
---
 hw/virtio/vhost-user.c    |  7 +++++++
 hw/virtio/vhost.c         | 10 ++++++++++
 include/hw/virtio/vhost.h |  1 +
 3 files changed, 18 insertions(+)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 1a7d53c..ca41728 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -531,6 +531,11 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
 
     vhost_user_write(dev, &msg, fds, fd_num);
 
+    if (!dev->mem_changed_req_sync) {
+        /* The update only add regions, skip the sync */
+        return 0;
+    }
+
     if (reply_supported) {
         return process_message_reply(dev, msg.request);
     } else {
@@ -541,6 +546,8 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
         vhost_user_get_features(dev, &features);
     }
 
+    dev->mem_changed_req_sync = false;
+
     return 0;
 }
 
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 3d0c807..e653067 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -303,7 +303,11 @@ static void vhost_dev_assign_memory(struct vhost_dev *dev,
         reg->guest_phys_addr = start_addr;
         reg->userspace_addr = uaddr;
         ++to;
+    } else {
+        /* Existing mapping updated, sync is required */
+        dev->mem_changed_req_sync = true;
     }
+
     assert(to <= dev->mem->nregions + 1);
     dev->mem->nregions = to;
 }
@@ -533,6 +537,7 @@ static void vhost_set_memory(MemoryListener *listener,
     } else {
         /* Remove old mapping for this memory, if any. */
         vhost_dev_unassign_memory(dev, start_addr, size);
+        dev->mem_changed_req_sync = true;
     }
     dev->mem_changed_start_addr = MIN(dev->mem_changed_start_addr, start_addr);
     dev->mem_changed_end_addr = MAX(dev->mem_changed_end_addr, start_addr + 
size - 1);
@@ -1126,6 +1131,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
     hdev->log_enabled = false;
     hdev->started = false;
     hdev->memory_changed = false;
+    hdev->mem_changed_req_sync = false;
     memory_listener_register(&hdev->memory_listener, &address_space_memory);
     QLIST_INSERT_HEAD(&vhost_devices, hdev, entry);
     return 0;
@@ -1301,6 +1307,10 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice 
*vdev)
     if (r < 0) {
         goto fail_features;
     }
+
+    /* First time the mem table is set, skip sync for completion */
+    hdev->mem_changed_req_sync = false;
+
     r = hdev->vhost_ops->vhost_set_mem_table(hdev, hdev->mem);
     if (r < 0) {
         VHOST_OPS_DEBUG("vhost_set_mem_table failed");
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index e433089..4bbf36a 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -55,6 +55,7 @@ struct vhost_dev {
     uint64_t log_size;
     Error *migration_blocker;
     bool memory_changed;
+    bool mem_changed_req_sync;
     hwaddr mem_changed_start_addr;
     hwaddr mem_changed_end_addr;
     const VhostOps *vhost_ops;
-- 
2.7.4