On 5/30/19 3:45 AM, Paolo Valente wrote: > > >> Il giorno 30 mag 2019, alle ore 10:29, Srivatsa S. Bhat <srivatsa@xxxxxxxxxxxxx> ha scritto: >> [...] >> >> Your fix held up well under my testing :) >> > > Great! > >> As for throughput, with low_latency = 1, I get around 1.4 MB/s with >> bfq (vs 1.6 MB/s with mq-deadline). This is a huge improvement >> compared to what it was before (70 KB/s). >> > > That's beautiful news! > > So, now we have the best of the two worlds: maximum throughput and > total control on I/O (including minimum latency for interactive and > soft real-time applications). Besides, no manual configuration > needed. Of course, this holds unless/until you find other flaws ... ;) > Indeed, that's awesome! :) >> With tracing on, the throughput is a bit lower (as expected I guess), >> about 1 MB/s, and the corresponding trace file >> (trace-waker-detection-1MBps) is available at: >> >> https://www.dropbox.com/s/3roycp1zwk372zo/bfq-traces.tar.gz?dl=0 >> > > Thank you for the new trace. I've analyzed it carefully, and, as I > imagined, this residual 12% throughput loss is due to a couple of > heuristics that occasionally get something wrong. Most likely, ~12% > is the worst-case loss, and if one repeats the tests, the loss may be > much lower in some runs. > Ah, I see. > I think it is very hard to eliminate this fluctuation while keeping > full I/O control. But, who knows, I might have some lucky idea in the > future. > :) > At any rate, since you pointed out that you are interested in > out-of-the-box performance, let me complete the context: in case > low_latency is left set, one gets, in return for this 12% loss, > a) at least 1000% higher responsiveness, e.g., 1000% lower start-up > times of applications under load [1]; > b) 500-1000% higher throughput in multi-client server workloads, as I > already pointed out [2]. > I'm very happy that you could solve the problem without having to compromise on any of the performance characteristics/features of BFQ! > I'm going to prepare complete patches. In addition, if ok for you, > I'll report these results on the bug you created. Then I guess we can > close it. > Sounds great! > [1] https://algo.ing.unimo.it/people/paolo/disk_sched/results.php > [2] https://www.linaro.org/blog/io-bandwidth-management-for-production-quality-services/ > >> Thank you so much for your tireless efforts in fixing this issue! >> > > I did enjoy working on this with you: your test case and your support > enabled me to make important improvements. So, thank you very much > for your collaboration so far, > Paolo My pleasure! :) Regards, Srivatsa VMware Photon OS
