On 2017/10/6 下午7:57, Michael Lyle wrote: > OK, here's some data: http://jar.lyle.org/~mlyle/writeback/ > > The complete test script is there to automate running writeback > scenarios--- NOTE DONT RUN WITHOUT EDITING THE DEVICES FOR YOUR > HARDWARE. > > Only one run each way, but they take 8-9 minutes to run, we can easily > get more ;) I compared patches 1-3 (which are uncontroversial) to > 1-5. > > Concerns I've heard: > > - The new patches will contend for I/O bandwidth with front-end writes: > > No: > 3 PATCHES: write: io=29703MB, bw=83191KB/s, iops=10398, runt=365618msec > vs > 5 PATCHES: write: io=29746MB, bw=86177KB/s, iops=10771, runt=353461msec > > It may actually be slightly better-- 3% or so. > > - The new patches will not improve writeback rate. > > No: > > 3 PATCHES: the active period of the test was 366+100=466 seconds, and > at the end there was 33.4G dirty. > 5 PATCHES: the active period of the test was 353+100=453 seconds, and > at the end there was 32.7G dirty. > > This is a moderate improvement. > > - The IO scheduler can combine the writes anyways so this type of > patch will not increase write queue merge. > > No: > > Average wrqm/s is 1525.4 in the 3 PATCHES dataset; average wrqm/s is > 1643.7 in the 5 PATCHES dataset. > > During the last 100 seconds, when ONLY WRITEBACK is occurring, wrqm is > 1398.0 in 3 PATCHES, and 1811.6 with 5 PATCHES. > > - Front-end latency will suffer: > > No: > > The datasets look the same to my eye. By far the worst thing is the > occasional 1000ms+ times the bcache goes to sleep in both scenarios, > contending for the writeback lock (not affected by these patches, but > an item for future work if I ever get to move on to a new topic). > > Conclusion: > > These patches provide a small but significant improvement in writeback > rates, that can be seen with careful testing that produces actual > sequential writeback. They lay the groundwork for further > improvements, through the use of plugging the block layer and to allow > accelerated writeback when the device is idle. > [snip] Hi Mike, Thank you for the detailed information! In your test, dirty data occupies 1/8 space of CACHEDEVICE, can I know exact sizes of the cache device and cached device, then I will set up a similar configuration on my machine, and try to reproduce the test. -- Coly Li
