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live migration: Serialize vmstate saving in stage 2 

The effect of this patch with current block migration is that its stage
2, ie. the first full walk-through of the block devices will be
performed completely before RAM migration starts. This ensures that
continuously changing RAM pages are not re-synchronized all the time
while block migration is not completed.

Future versions of block migration which will respect the specified
downtime will generate a different pattern: After RAM migration has
started as well, block migration may also continue to inject dirty
blocks into the RAM stream once it detects that the number of pending
blocks would extend the downtime unacceptably.

Note that all this relies on the current registration order: block
before RAM migration.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Jan Kiszka 2009-12-01 15:19:55 +01:00 committed by Anthony Liguori
parent 792773b225
commit 90697be889
1 changed files with 8 additions and 1 deletions
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9
savevm.c
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@ -1321,7 +1321,14 @@ int qemu_savevm_state_iterate(Monitor *mon, QEMUFile *f)
qemu_put_byte(f, QEMU_VM_SECTION_PART);
qemu_put_be32(f, se->section_id);
ret &= !!se->save_live_state(mon, f, QEMU_VM_SECTION_PART, se->opaque);
ret = se->save_live_state(mon, f, QEMU_VM_SECTION_PART, se->opaque);
if (!ret) {
/* Do not proceed to the next vmstate before this one reported
completion of the current stage. This serializes the migration
and reduces the probability that a faster changing state is
synchronized over and over again. */
break;
}
}
if (ret)