Hi Paolo, I've looked at your WIP branch as of 4.11.0-bfq-mq-rc4-00155-gbce0818 and did some fio tests to compare the behavior to CFQ.
My understanding is that bfq-mq is supposed to be merged sooner or later and then it will be the only reasonable I/O scheduler with blk-mq for rotational devices. Hence I think it is interesting to see what to expect performance-wise in comparison to CFQ which is usually used for such devices with the legacy block layer. I've just done simple tests iterating over number of jobs (1-8 as the test system had 8 CPUs) for all (random/sequential) read/write patterns. Fixed set of fio parameters used were '-size=5G --group_reporting --ioengine=libaio --direct=1 --iodepth=1 --runtime=10'. I've done 10 runs for each such configuration. The device used was an older SAMSUNG HD103SJ 1TB disk, SATA attached. Results that stick out the most are those for sequential reads and sequential writes: * sequential reads [0] - cfq, intel_pstate driver, powersave governor [1] - bfq_mq, intel_pstate driver, powersave governor jo [0] [1] bs mean stddev mean stddev 1 & 17060.300 & 77.090 & 17657.500 & 69.602 2 & 15318.200 & 28.817 & 10678.000 & 279.070 3 & 15403.200 & 42.762 & 9874.600 & 93.436 4 & 14521.200 & 624.111 & 9918.700 & 226.425 5 & 13893.900 & 144.354 & 9485.000 & 109.291 6 & 13065.300 & 180.608 & 9419.800 & 75.043 7 & 12169.600 & 95.422 & 9863.800 & 227.662 8 & 12422.200 & 215.535 & 15335.300 & 245.764 * sequential writes [0] - cfq, intel_pstate driver, powersave governor [1] - bfq_mq, intel_pstate driver, powersave governor jo [0] [1] bs mean stddev mean stddev 1 & 14171.300 & 80.796 & 14392.500 & 182.587 2 & 13520.000 & 88.967 & 9565.400 & 119.400 3 & 13396.100 & 44.936 & 9284.000 & 25.122 4 & 13139.800 & 62.325 & 8846.600 & 45.926 5 & 12942.400 & 45.729 & 8568.700 & 35.852 6 & 12650.600 & 41.283 & 8275.500 & 199.273 7 & 12475.900 & 43.565 & 8252.200 & 33.145 8 & 12307.200 & 43.594 & 13617.500 & 127.773 With performance instead of powersave governor results were (expectedly) higher but the pattern was the same -- bfq-mq shows a "dent" for tests with 2-7 fio jobs. At the moment I have no explanation for this behavior. Regards, Andreas
