migration: postcopy_blocktime documentation
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Signed-off-by: Alexey Perevalov <a.perevalov@samsung.com> Reviewed-by: Juan Quintela <quintela@redhat.com> Signed-off-by: Juan Quintela <quintela@redhat.com>
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			@ -401,6 +401,20 @@ will now cause the transition from precopy to postcopy.
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It can be issued immediately after migration is started or any
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time later on.  Issuing it after the end of a migration is harmless.
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Blocktime is a postcopy live migration metric, intended to show how
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long the vCPU was in state of interruptable sleep due to pagefault.
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That metric is calculated both for all vCPUs as overlapped value, and
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separately for each vCPU. These values are calculated on destination
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side.  To enable postcopy blocktime calculation, enter following
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command on destination monitor:
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``migrate_set_capability postcopy-blocktime on``
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Postcopy blocktime can be retrieved by query-migrate qmp command.
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postcopy-blocktime value of qmp command will show overlapped blocking
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time for all vCPU, postcopy-vcpu-blocktime will show list of blocking
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time per vCPU.
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.. note::
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  During the postcopy phase, the bandwidth limits set using
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  ``migrate_set_speed`` is ignored (to avoid delaying requested pages that
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