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>

1 files changed, 18 insertions, 30 deletions

diff --git a/arch_init.c b/arch_init.c
index fad1c40..af1ae9f 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -582,12 +582,9 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
 
 static int ram_save_iterate(QEMUFile *f, void *opaque)
 {
-    uint64_t bytes_transferred_last;
-    double bwidth = 0;
     int ret;
     int i;
-    uint64_t expected_downtime;
-    MigrationState *s = migrate_get_current();
+    int64_t t0;
 
     qemu_mutex_lock_ramlist();
 
@@ -595,9 +592,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
         reset_ram_globals();
     }
 
-    bytes_transferred_last = bytes_transferred;
-    bwidth = qemu_get_clock_ns(rt_clock);
-
+    t0 = qemu_get_clock_ns(rt_clock);
     i = 0;
     while ((ret = qemu_file_rate_limit(f)) == 0) {
         int bytes_sent;
@@ -615,7 +610,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
            iterations
         */
         if ((i & 63) == 0) {
-            uint64_t t1 = (qemu_get_clock_ns(rt_clock) - bwidth) / 1000000;
+            uint64_t t1 = (qemu_get_clock_ns(rt_clock) - t0) / 1000000;
             if (t1 > MAX_WAIT) {
                 DPRINTF("big wait: %" PRIu64 " milliseconds, %d iterations\n",
                         t1, i);
@@ -629,31 +624,10 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
         return ret;
     }
 
-    bwidth = qemu_get_clock_ns(rt_clock) - bwidth;
-    bwidth = (bytes_transferred - bytes_transferred_last) / bwidth;
-
-    /* if we haven't transferred anything this round, force
-     * expected_downtime to a very high value, but without
-     * crashing */
-    if (bwidth == 0) {
-        bwidth = 0.000001;
-    }
-
     qemu_mutex_unlock_ramlist();
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
 
-    expected_downtime = ram_save_remaining() * TARGET_PAGE_SIZE / bwidth;
-    DPRINTF("ram_save_live: expected(%" PRIu64 ") <= max(" PRIu64 ")?\n",
-            expected_downtime, migrate_max_downtime());
-
-    if (expected_downtime <= migrate_max_downtime()) {
-        migration_bitmap_sync();
-        expected_downtime = ram_save_remaining() * TARGET_PAGE_SIZE / bwidth;
-        s->expected_downtime = expected_downtime / 1000000; /* ns -> ms */
-
-        return expected_downtime <= migrate_max_downtime();
-    }
-    return 0;
+    return i;
 }
 
 static int ram_save_complete(QEMUFile *f, void *opaque)
@@ -683,6 +657,19 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
     return 0;
 }
 
+static uint64_t ram_save_pending(QEMUFile *f, void *opaque, uint64_t max_size)
+{
+    uint64_t remaining_size;
+
+    remaining_size = ram_save_remaining() * TARGET_PAGE_SIZE;
+
+    if (remaining_size < max_size) {
+        migration_bitmap_sync();
+        remaining_size = ram_save_remaining() * TARGET_PAGE_SIZE;
+    }
+    return remaining_size;
+}
+
 static int load_xbzrle(QEMUFile *f, ram_addr_t addr, void *host)
 {
     int ret, rc = 0;
@@ -869,6 +856,7 @@ SaveVMHandlers savevm_ram_handlers = {
     .save_live_setup = ram_save_setup,
     .save_live_iterate = ram_save_iterate,
     .save_live_complete = ram_save_complete,
+    .save_live_pending = ram_save_pending,
     .load_state = ram_load,
     .cancel = ram_migration_cancel,
 };