On Mon, Aug 19, 2013 at 09:59:09AM +0800, Miao Xie wrote: > Hi, everyone > > On Thu, 8 Aug 2013 16:54:18 +0800, Fengguang Wu wrote: > > This helps performance on moderately dense random reads on SSD. > > > > Transaction-Per-Second numbers provided by Taobao: > > > > QPS case > > ------------------------------------------------------- > > 7536 disable context readahead totally > > w/ patch: 7129 slower size rampup and start RA on the 3rd read > > 6717 slower size rampup > > w/o patch: 5581 unmodified context readahead > > > > Before, readahead will be started whenever reading page N+1 when it > > happen to read N recently. After patch, we'll only start readahead > > when *three* random reads happen to access pages N, N+1, N+2. The > > probability of this happening is extremely low for pure random reads, > > unless they are very dense, which actually deserves some readahead. > > > > Also start with a smaller readahead window. The impact to interleaved > > sequential reads should be small, because for a long run stream, the > > the small readahead window rampup phase is negletable. > > > > The context readahead actually benefits clustered random reads on HDD > > whose seek cost is pretty high. However as SSD is increasingly used > > for random read workloads it's better for the context readahead to > > concentrate on interleaved sequential reads. > > > > Another SSD rand read test from Miao > > > > # file size: 2GB > > # read IO amount: 625MB > > sysbench --test=fileio \ > > --max-requests=10000 \ > > --num-threads=1 \ > > --file-num=1 \ > > --file-block-size=64K \ > > --file-test-mode=rndrd \ > > --file-fsync-freq=0 \ > > --file-fsync-end=off run > > > > shows the performance of btrfs grows up from 69MB/s to 121MB/s, > > ext4 from 104MB/s to 121MB/s. > > I did the same test on the hard disk recently, > for btrfs, there is ~5% regression(10.65MB/s -> 10.09MB/s), > for ext4, the performance grows up a bit.(9.98MB/s -> 10.04MB/s). > (I run the test for 4 times, and the above result is the average of the test.) > > Any comment? Thanks for the tests! Minor regressions on the HDD cases are expected. Since random read workloads are migrating to SSD as it becomes cheaper and larger, it seems a good tradeoff to optimize for random read performance on SSD. Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>