pgbench: Stabilise pgbench results

Signed-off-by: Mel Gorman <mgorman@suse.de>
pgbench: Distinguish between cache hot/cold tests

Signed-off-by: Mel Gorman <mgorman@suse.de>
pgbench: Add xlarge configs

Signed-off-by: Mel Gorman <mgorman@suse.de>
pgbench: Report on stalls

Signed-off-by: Mel Gorman <mgorman@suse.de>