On Wed, Oct 05, 2016 at 09:57:22PM +0200, Paolo Valente wrote: > > > Il giorno 05 ott 2016, alle ore 21:08, Shaohua Li <shli@xxxxxx> ha scritto: > > > > On Wed, Oct 05, 2016 at 11:30:53AM -0700, Shaohua Li wrote: > >> On Wed, Oct 05, 2016 at 10:49:46AM -0400, Tejun Heo wrote: > >>> Hello, Paolo. > >>> > >>> On Wed, Oct 05, 2016 at 02:37:00PM +0200, Paolo Valente wrote: > >>>> In this respect, for your generic, unpredictable scenario to make > >>>> sense, there must exist at least one real system that meets the > >>>> requirements of such a scenario. Or, if such a real system does not > >>>> yet exist, it must be possible to emulate it. If it is impossible to > >>>> achieve this last goal either, then I miss the usefulness > >>>> of looking for solutions for such a scenario. > >>>> > >>>> That said, let's define the instance(s) of the scenario that you find > >>>> most representative, and let's test BFQ on it/them. Numbers will give > >>>> us the answers. For example, what about all or part of the following > >>>> groups: > >>>> . one cyclically doing random I/O for some second and then sequential I/O > >>>> for the next seconds > >>>> . one doing, say, quasi-sequential I/O in ON/OFF cycles > >>>> . one starting an application cyclically > >>>> . one playing back or streaming a movie > >>>> > >>>> For each group, we could then measure the time needed to complete each > >>>> phase of I/O in each cycle, plus the responsiveness in the group > >>>> starting an application, plus the frame drop in the group streaming > >>>> the movie. In addition, we can measure the bandwidth/iops enjoyed by > >>>> each group, plus, of course, the aggregate throughput of the whole > >>>> system. In particular we could compare results with throttling, BFQ, > >>>> and CFQ. > >>>> > >>>> Then we could write resulting numbers on the stone, and stick to them > >>>> until something proves them wrong. > >>>> > >>>> What do you (or others) think about it? > >>> > >>> That sounds great and yeah it's lame that we didn't start with that. > >>> Shaohua, would it be difficult to compare how bfq performs against > >>> blk-throttle? > >> > >> I had a test of BFQ. I'm using BFQ found at > >> https://urldefense.proofpoint.com/v2/url?u=http-3A__algogroup.unimore.it_people_paolo_disk-5Fsched_sources.php&d=DQIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=X13hAPkxmvBro1Ug8vcKHw&m=zB09S7v2QifXXTa6f2_r6YLjiXq3AwAi7sqO4o2UfBQ&s=oMKpjQMXfWmMwHmANB-Qnrm2EdERzz9Oef7jcLkbyFg&e= . version is > >> 4.7.0-v8r3. It's a LSI SSD, queue depth 32. I use default setting. fio script > >> is: > >> > >> [global] > >> ioengine=libaio > >> direct=1 > >> readwrite=randread > >> bs=4k > >> runtime=60 > >> time_based=1 > >> file_service_type=random:36 > >> overwrite=1 > >> thread=0 > >> group_reporting=1 > >> filename=/dev/sdb > >> iodepth=1 > >> numjobs=8 > >> > >> [groupA] > >> prio=2 > >> > >> [groupB] > >> new_group > >> prio=6 > >> > >> I'll change iodepth, numjobs and prio in different tests. result unit is MB/s. > >> > >> iodepth=1 numjobs=1 prio 4:4 > >> CFQ: 28:28 BFQ: 21:21 deadline: 29:29 > >> > >> iodepth=8 numjobs=1 prio 4:4 > >> CFQ: 162:162 BFQ: 102:98 deadline: 205:205 > >> > >> iodepth=1 numjobs=8 prio 4:4 > >> CFQ: 157:157 BFQ: 81:92 deadline: 196:197 > >> > >> iodepth=1 numjobs=1 prio 2:6 > >> CFQ: 26.7:27.6 BFQ: 20:6 deadline: 29:29 > >> > >> iodepth=8 numjobs=1 prio 2:6 > >> CFQ: 166:174 BFQ: 139:72 deadline: 202:202 > >> > >> iodepth=1 numjobs=8 prio 2:6 > >> CFQ: 148:150 BFQ: 90:77 deadline: 198:197 > > > > More tests: > > > > iodepth=8 numjobs=1 prio 2:6, group A has 50M/s limit > > CFQ:51:207 BFQ: 51:45 deadline: 51:216 > > > > iodepth=1 numjobs=1 prio 2:6, group A bs=4k, group B bs=64k > > CFQ:25:249 BFQ: 23:42 deadline: 26:251 > > > > A true proportional share scheduler like BFQ works under the > assumption to be the only limiter of the bandwidth of its clients. > And the availability of such a scheduler should apparently make > bandwidth limiting useless: once you have a mechanism that allows you > to give each group the desired fraction of the bandwidth, and to > redistribute excess bandwidth seamlessly when needed, what do you need > additional limiting for? > > But I'm not expert of any possible system configuration or > requirement. So, if you have practical examples, I would really > appreciate them. And I don't think it will be difficult to see what > goes wrong in BFQ with external bw limitation, and to fix the > problem. I think the test emulates a very common configuration. We assign more IO resources to high priority workload. But such workload doesn't always dispatch enough io. That's why I set a rate limit. When this happend, we hope low priority workload uses the disk bandwidth. That's the whole point of disk sharing. Thanks, Shaohua -- 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
