Re: [Qemu-devel] [PATCH 22/30] migration: unfold rest of migrate_fd_put_ready() into thread

[Paolo Bonzini]

Il 18/10/2012 10:39, Paolo Bonzini ha scritto:
> in this function.  Perhaps it is better if you make an invariant that
> the loop is entered and exited with the BQL taken, and it is only
> unlocked in the middle.  It makes sense once you fold everything in
> migration.c.

i.e. this:

diff --git a/migration.c b/migration.c
index 554d79a..bd9fe2d 100644
--- a/migration.c
+++ b/migration.c
@@ -661,23 +661,18 @@ static void *buffered_file_thread(void *opaque)
     ret = qemu_savevm_state_begin(m->file, &m->params);
     if (ret < 0) {
         DPRINTF("failed, %d\n", ret);
-        qemu_mutex_unlock_iothread();
         goto out;
     }
-    qemu_mutex_unlock_iothread();
 
     while (true) {
         int64_t current_time = qemu_get_clock_ms(rt_clock);
         uint64_t pending_size;
 
-        qemu_mutex_lock_iothread();
         if (m->state != MIG_STATE_ACTIVE) {
             DPRINTF("put_ready returning because of non-active state\n");
-            qemu_mutex_unlock_iothread();
             break;
         }
         if (m->complete) {
-            qemu_mutex_unlock_iothread();
             break;
         }
         if (s->bytes_xfer < s->xfer_limit) {
@@ -687,7 +682,6 @@ static void *buffered_file_thread(void *opaque)
             if (pending_size && pending_size >= max_size) {
                 ret = qemu_savevm_state_iterate(m->file);
                 if (ret < 0) {
-                    qemu_mutex_unlock_iothread();
                     break;
                 }
             } else {
@@ -708,7 +702,6 @@ static void *buffered_file_thread(void *opaque)
                 printf("vm_stop 2 %ld\n", end_time - start_time);
                 ret = qemu_savevm_state_complete(m->file);
                 if (ret < 0) {
-                    qemu_mutex_unlock_iothread();
                     break;
                 } else {
                     end_time = qemu_get_clock_ms(rt_clock);
@@ -729,8 +722,8 @@ static void *buffered_file_thread(void *opaque)
                 last_round = true;
             }
         }
-        qemu_mutex_unlock_iothread();
 
+        qemu_mutex_unlock_iothread();
         if (current_time >= initial_time + BUFFER_DELAY) {
             uint64_t transferred_bytes = s->bytes_xfer;
             uint64_t time_spent = current_time - initial_time;
@@ -749,9 +742,11 @@ static void *buffered_file_thread(void *opaque)
             usleep((initial_time + BUFFER_DELAY - current_time)*1000);
         }
         buffered_flush(s);
+        qemu_mutex_lock_iothread();
     }
 
 out:
+    qemu_mutex_unlock_iothread();
     if (ret < 0) {
         migrate_fd_error(m);
     }


BTW the completion (basically the "else" starting at "int old_vm_running =
runstate_is_running()" looks much nicer in a separate function, like:

            if (pending_size && pending_size >= max_size) {
                ret = qemu_savevm_state_iterate(m->file);
            } else {
                ret = migration_complete(m);
                last_round = true;
            }
            if (ret < 0) {
                break;
            }

Paolo