migration: Wake rate limiting for urgent requests
Rate limiting sleeps the migration thread for a while when it runs
out of bandwidth; but sometimes we want to wake up to get on with
something more urgent (like a postcopy request). Here we use
a semaphore with a timedwait instead of a simple sleep; Incrementing
the sempahore will wake it up sooner. Anything that consumes
these urgent events must decrement the sempahore.
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <
20180613102642.23995-3-dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>