The TBF policy is not aimed to provide improved performance, it achieves rate limit through I/O throttle. When I/O is throttling, it could not make full use of system resources even there are some ideal I/O service threads and spare disk I/O bandwidth. But for some use cases, it needs to have the ability to allocate spare capacity to the workloads or background jobs. In order to ensure efficient utilization of I/O resource, we propose a dependency rule strategy. The command of a dependency rule is shown as following:

start ruleB <matchCondition> deprule=ruleA lowerrate=$r1 upperrate=$r2

Where deprule represents the rule name of the dependent rule, which means, 'ruleB' depends on 'ruleA' ; the key 'lowerrate' indicates the lower bound of RPC rate limited value while the key 'upperrate' indicates the upper bound of RPC rate limited value. The principle is that the real RPC rate limited value of a rule is dynamically adjusted between the lowerrate and upperrate to obtain more I/O bandwidth according to the spare I/O capacity that its dependent rule does not make full use of.