On 10 Apr 2017, Shaohua Li stated: > On Wed, Apr 05, 2017 at 03:13:48PM +0100, Nix wrote: >> So you'd expect write rates on a RAID-5 array to be higher than write rates on a >> single spinning-rust disk, right? Because, even with Shaohua's commit >> 765d704db1f583630d52 applied atop 4.10, I see little sign of it. Does this >> commit depend upon something else to stop death by seeking with >> group_thread_cnt > 0? It didn't look like it to me... >> >> The results Shaohua showed in the original commit were very impressive, but for >> the life of me I can't figure out how to get anything like them. > > That only works well with large iodepth. For single write, we are still far > from the BW in theory. I actually wrote in the commit log: > > "We are pretty close to the maximum bandwidth in the large iodepth > iodepth case. The performance gap of small iodepth sequential write > between software raid and theory value is still very big though, because > we don't have an efficient pipeline." Ah right, I missed the significance of that. So this helps only if you have multiple simultaneous multithreaded/async I/Os to the same file at the same time? Damn, no help in any of my common use cases yet :( :( :( except maybe massively-parallel compiles, but they are never write-bound except when linking, and *that* is serial. I guess I have to wait and hope for a better pipeline :) -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
