On 2017/10/6 下午5:20, Michael Lyle wrote: > Coly-- > > I did not say the result from the changes will be random. > > I said the result from your test will be random, because where the > writeback position is making non-contiguous holes in the data is > nondeterministic-- it depends where it is on the disk at the instant > that writeback begins. There is a high degree of dispersion in the > test scenario you are running that is likely to exceed the differences > from my patch. Hi Mike, I did the test quite carefully. Here is how I ran the test, - disable writeback by echo 0 to writeback_runing. - write random data into cache to full or half size, then stop the I/O immediately. - echo 1 to writeback_runing to start writeback - and record performance data at once It might be random position where the writeback starts, but there should not be too much difference of statistical number of the continuous blocks (on cached device). Because fio just send random 512KB blocks onto cache device, the statistical number of contiguous blocks depends on cache device vs. cached device size, and how full the cache device is occupied. Indeed, I repeated some tests more than once (except the md raid5 and md raid0 configurations), the results are quite sable when I see the data charts, no big difference. If you feel the performance result I provided is problematic, it would be better to let the data talk. You need to show your performance test number to prove that the bio reorder patches are helpful for general workloads, or at least helpful to many typical workloads. Let the data talk. Thanks. -- Coly Li
