Hi Shaohua, all, at last, I started testing your io.low limit for blk-throttle. One of the things I'm interested in is how good throttling is in achieving a high throughput in the presence of realistic, variable workloads.
However, I seem to have bumped into a totally different problem. The io.low parameter doesn't seem to guarantee what I understand it is meant to guarantee: minimum per-group bandwidths. For example, with - one group, the interfered, containing one process that does sequential reads with fio - io.low set to 100MB/s for the interfered - six other groups, the interferers, with each interferer containing one process doing sequential read with fio - io.low set to 10MB/s for each interferer - the workload executed on an SSD, with a 500MB/s of overall throughput the interfered gets only 75MB/s. In particular, the throughput of the interfered becomes lower and lower as the number of interferers is increased. So you can make it become even much lower than the 75MB/s in the example above. There seems to be no control on bandwidth. Am I doing something wrong? Or did I simply misunderstand the goal of io.low, and the only parameter for guaranteeing the desired bandwidth to a group is io.max (to be used indirectly, by limiting the bandwidth of the interferers)? If useful for you, you can reproduce the above test very quickly, by using the S suite [1] and typing: cd thr-lat-with-interference sudo ./thr-lat-with-interference.sh -b t -w 100000000 -W "10000000 10000000 10000000 10000000 10000000 10000000" -n 6 -T "read read read read read read" -R "0 0 0 0 0 0" Looking forward to your feedback, Paolo [1]
