Hello, Shaohua. On Mon, Nov 14, 2016 at 02:22:17PM -0800, Shaohua Li wrote: > Unfortunately it's very hard to determine if a cgroup is real idle. This > patch uses the 'think time check' idea from CFQ for the purpose. Please > note, the idea doesn't work for all workloads. For example, a workload > with io depth 8 has disk utilization 100%, hence think time is 0, eg, > not idle. But the workload can run higher bandwidth with io depth 16. > Compared to io depth 16, the io depth 8 workload is idle. We use the > idea to roughly determine if a cgroup is idle. Hmm... I'm not sure thinktime is the best measure here. Think time is used by cfq mainly to tell the likely future behavior of a workload so that cfq can take speculative actions on the prediction. However, given that the implemented high limit behavior tries to provide a certain level of latency target, using the predictive thinktime to regulate behavior might lead to too unpredictable behaviors. Moreover, I don't see why we need to bother with predictions anyway. cfq needed it but I don't think that's the case for blk-throtl. It can just provide idle threshold where a cgroup which hasn't issued an IO over that threshold is considered idle. That'd be a lot easier to understand and configure from userland while providing a good enough mechanism to prevent idle cgroups from clamping down utilization for too long. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
