Reviewed-by: Dr. David Alan Gilbert <>
Signed-off-by: Alexey Perevalov <>
Reviewed-by: Juan Quintela <>
Signed-off-by: Juan Quintela <>
 docs/devel/migration.rst | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/docs/devel/migration.rst b/docs/devel/migration.rst
index 9d1b765..18cd952 100644
--- a/docs/devel/migration.rst
+++ b/docs/devel/migration.rst
@@ -401,6 +401,20 @@ will now cause the transition from precopy to postcopy.
 It can be issued immediately after migration is started or any
 time later on.  Issuing it after the end of a migration is harmless.
+Blocktime is a postcopy live migration metric, intended to show how
+long the vCPU was in state of interruptable sleep due to pagefault.
+That metric is calculated both for all vCPUs as overlapped value, and
+separately for each vCPU. These values are calculated on destination
+side.  To enable postcopy blocktime calculation, enter following
+command on destination monitor:
+``migrate_set_capability postcopy-blocktime on``
+Postcopy blocktime can be retrieved by query-migrate qmp command.
+postcopy-blocktime value of qmp command will show overlapped blocking
+time for all vCPU, postcopy-vcpu-blocktime will show list of blocking
+time per vCPU.
 .. note::
   During the postcopy phase, the bandwidth limits set using
   ``migrate_set_speed`` is ignored (to avoid delaying requested pages that

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