> Il giorno 15 ott 2018, alle ore 17:02, Bart Van Assche <bvanassche@xxxxxxx> ha scritto: > > On Mon, 2018-10-15 at 16:10 +0200, Linus Walleij wrote: >> + * For blk-mq devices, we default to using: >> + * - "none" for multiqueue devices (nr_hw_queues != 1) >> + * - "bfq", if available, for single queue devices >> + * - "mq-deadline" if "bfq" is not available for single queue devices >> + * - "none" for single queue devices as well as last resort > > For SATA SSDs nr_hw_queues == 1 so this patch will also affect these SSDs. > Since this patch is an attempt to improve performance, I'd like to see > measurement data for one or more recent SATA SSDs before a decision is > taken about what to do with this patch. > Hi Bart, as I just wrote to Jens I don't think we need this test any longer. To save you one hope, I'll paste my reply to Jens below. Anyway, it is very easy to do the tests you ask: - take a kernel containing the last bfq commits, such as for-next - do, e.g., git clone https://github.com/Algodev-github/S.git cd S/run_multiple_benchmarks sudo ./run_main_benchmarks.sh "throughput replayed-startup" "bfq none" - compare results Of course, do not do it for multi-queue devices or single-queues devices, on steroids, that do 400-500 KIOPS. I'll see if I can convince someone to repeat these tests with a recent SSD. And here is again my reply to Jens, which I think holds for your repeated objection too. I tested bfq on virtually every device in the range from few hundred of IOPS to 50-100KIOPS. Then, through the public script I already mentioned, I found the maximum number of IOPS that bfq can handle: about 400K with a commodity CPU. In particular, in all my tests with real hardware, bfq performance - is not even comparable to that of any of the other scheduler, in terms of responsiveness, latency for real-time applications, ability to provide strong bandwidth guarantees, ability to boost throughput while guaranteeing bandwidths; - is a little worse than the other schedulers for only one test, on only some hardware: total throughput with random reads, were it may lose up to 10-15% of throughput. Of course, the schedulers that reach a higher throughput leave the machine unusable during the test. So I really cannot see a reason why bfq could do worse than any of these other schedulers for some single-queue device (conservatively) below 300KIOPS. Finally, since, AFAICT, single-queue devices doing 400+ KIOPS are probably less than 1% of all the single-queue storage around (USB drives, HDDs, eMMC, standard SSDs, ...), by sticking to mq-deadline we are sacrificing 99% of the hardware, to help 1% of the hardware for one kind of test cases. Thanks, Paolo > Thanks, > > Bart. >
