migration: Tracepoint change in postcopy-run bottom half

Remove the old two tracepoints and they're even near each other:

    trace_loadvm_postcopy_handle_run_cpu_sync()
    trace_loadvm_postcopy_handle_run_vmstart()

Add trace_loadvm_postcopy_handle_run_bh() with a finer granule trace.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20220301083925.33483-4-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/savevm.c

@@ -2006,13 +2006,19 @@ static void loadvm_postcopy_handle_run_bh(void *opaque)
     Error *local_err = NULL;
     MigrationIncomingState *mis = opaque;
 
+    trace_loadvm_postcopy_handle_run_bh("enter");
+
     /* TODO we should move all of this lot into postcopy_ram.c or a shared code
      * in migration.c
      */
     cpu_synchronize_all_post_init();
 
+    trace_loadvm_postcopy_handle_run_bh("after cpu sync");
+
     qemu_announce_self(&mis->announce_timer, migrate_announce_params());
 
+    trace_loadvm_postcopy_handle_run_bh("after announce");
+
     /* Make sure all file formats flush their mutable metadata.
      * If we get an error here, just don't restart the VM yet. */
     bdrv_invalidate_cache_all(&local_err);
@@ -2022,9 +2028,7 @@ static void loadvm_postcopy_handle_run_bh(void *opaque)
         autostart = false;
     }
 
-    trace_loadvm_postcopy_handle_run_cpu_sync();
-
-    trace_loadvm_postcopy_handle_run_vmstart();
+    trace_loadvm_postcopy_handle_run_bh("after invalidate cache");
 
     dirty_bitmap_mig_before_vm_start();
 
@@ -2037,6 +2041,8 @@ static void loadvm_postcopy_handle_run_bh(void *opaque)
     }
 
     qemu_bh_delete(mis->bh);
+
+    trace_loadvm_postcopy_handle_run_bh("return");
 }
 
 /* After all discards we can start running and asking for pages */

migration/trace-events

@@ -16,8 +16,7 @@ loadvm_handle_recv_bitmap(char *s) "%s"
 loadvm_postcopy_handle_advise(void) ""
 loadvm_postcopy_handle_listen(const char *str) "%s"
 loadvm_postcopy_handle_run(void) ""
-loadvm_postcopy_handle_run_cpu_sync(void) ""
-loadvm_postcopy_handle_run_vmstart(void) ""
+loadvm_postcopy_handle_run_bh(const char *str) "%s"
 loadvm_postcopy_handle_resume(void) ""
 loadvm_postcopy_ram_handle_discard(void) ""
 loadvm_postcopy_ram_handle_discard_end(void) ""