savevm: New save live migration method: pending

Code just now does (simplified for clarity)

    if (qemu_savevm_state_iterate(s->file) == 1) {
       vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
       qemu_savevm_state_complete(s->file);
    }

Problem here is that qemu_savevm_state_iterate() returns 1 when it
knows that remaining memory to sent takes less than max downtime.

But this means that we could end spending 2x max_downtime, one
downtime in qemu_savevm_iterate, and the other in
qemu_savevm_state_complete.

Changed code to:

    pending_size = qemu_savevm_state_pending(s->file, max_size);
    DPRINTF("pending size %lu max %lu\n", pending_size, max_size);
    if (pending_size >= max_size) {
        ret = qemu_savevm_state_iterate(s->file);
     } else {
        vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
        qemu_savevm_state_complete(s->file);
     }

So what we do is: at current network speed, we calculate the maximum
number of bytes we can sent: max_size.

Then we ask every save_live section how much they have pending.  If
they are less than max_size, we move to complete phase, otherwise we
do an iterate one.

This makes things much simpler, because now individual sections don't
have to caluclate the bandwidth (it was implossible to do right from
there).

Signed-off-by: Juan Quintela <quintela@redhat.com>

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 3 insertions, 1 deletions

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 92190f2afd..9571ec532c 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -81,7 +81,7 @@ void migrate_fd_connect(MigrationState *s);
 
 ssize_t migrate_fd_put_buffer(MigrationState *s, const void *data,
                               size_t size);
-void migrate_fd_put_ready(MigrationState *s);
+bool migrate_fd_put_ready(MigrationState *s, uint64_t max_size);
 int migrate_fd_close(MigrationState *s);
 
 void add_migration_state_change_notifier(Notifier *notify);
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 623af0a29a..f27276c2d8 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -35,6 +35,7 @@ typedef struct SaveVMHandlers {
     int (*save_live_setup)(QEMUFile *f, void *opaque);
     int (*save_live_iterate)(QEMUFile *f, void *opaque);
     int (*save_live_complete)(QEMUFile *f, void *opaque);
+    uint64_t (*save_live_pending)(QEMUFile *f, void *opaque, uint64_t max_size);
     void (*cancel)(void *opaque);
     LoadStateHandler *load_state;
     bool (*is_active)(void *opaque);
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 8eaa4707a0..28a783e2be 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -78,6 +78,7 @@ int qemu_savevm_state_begin(QEMUFile *f,
 int qemu_savevm_state_iterate(QEMUFile *f);
 int qemu_savevm_state_complete(QEMUFile *f);
 void qemu_savevm_state_cancel(QEMUFile *f);
+uint64_t qemu_savevm_state_pending(QEMUFile *f, uint64_t max_size);
 int qemu_loadvm_state(QEMUFile *f);
 
 /* SLIRP */