It depends on the sharding granularity. If you choose a low sharding ratio, then you waste a whole core, but that's assuming 1:1 shards to cores. If you shatter the search space using a large multiple of the number of cores, e.g. 1000:1, then shuffle the shards and have each core pick a shard off the queue, if any core ever gets stuck with a bad shard (i.e., conflict), it discards and picks a new one off the queue. This requires no communication and ensures all cores stay hot. I guess you might also need some preprocessing to remove trivially-conflicting shards.