On 2017/1/12 下午11:09, Sagi Grimberg wrote: > Hey Coly, > >> Also I receive reports from users that raid1 performance is desired when >> it is built on NVMe SSDs as a cache (maybe bcache or dm-cache). I am >> working on some raid1 performance improvement (e.g. new raid1 I/O >> barrier and lockless raid1 I/O submit), and have some more ideas to >> discuss. > > Do you have some performance measurements to share? > > Mike used null devices to simulate very fast devices which > led to nice performance enhancements in dm-multipath code. I have several performance data of raid1 and raid0, which is still work in progress. - md raid1 Current md raid1 read performance is not ideal. A raid1 with 2 NVMe SSD, only observe 2.6GB/s throughput for multi I/O and depth reading. Most of the time spending on I/O barrier locking. Now I am working on a lockless I/O submit patch (the original idea is from Hannes Reinecke), which improves reading throughput to 4.7~5GB/s. When using md raid1 as a cache device, reading performance improvement is critical. On my hardware, the ideal reading throughput of 2 NVMe is 6GB/s, currently the reading performance number is 4.7~5GB/s, still have a little some space to improve. - md raid0 People reports on linux-raid mailing list that DISCARD/TRIM performance on raid0 is slow. In my reproducing, a raid0 built by 4x3TB NVMe SSD, formatting a XFS volume on top of it takes 306 seconds. Most of the time is inside md raid0 code to issue DISCARD/TRIM request in chunk size range. I compose a POC patch to re-combine a large DISCARD/TRIM command into per-device request, which reduces the formatting time to 15 seconds. Now I work on patch simplifying by the suggestions from upstream maintainers. For raid1, currently most of feed backs are from read performance. Coly -- 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
