On Fri, Jun 19, 2009 at 03:04:36AM +0800, Andrew Morton wrote: > On Sun, 7 Jun 2009 06:45:38 +0800 > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > > > > > Do you have a place where the raw blktrace data can be retrieved for > > > > more in-depth analysis? > > > > > > I think your comment is really adequate. In another thread, Wu Fengguang pointed > > > out the same issue. > > > I and Wu also wait his analysis. > > > > And do it with a large readahead size :) > > > > Alan, this was my analysis: > > > > : Hifumi, can you help retest with some large readahead size? > > : > > : Your readahead size (128K) is smaller than your max_sectors_kb (256K), > > : so two readahead IO requests get merged into one real IO, that means > > : half of the readahead requests are delayed. > > > > ie. two readahead requests get merged and complete together, thus the effective > > IO size is doubled but at the same time it becomes completely synchronous IO. > > > > : > > : The IO completion size goes down from 512 to 256 sectors: > > : > > : before patch: > > : 8,0 3 177955 50.050313976 0 C R 8724991 + 512 [0] > > : 8,0 3 177966 50.053380250 0 C R 8725503 + 512 [0] > > : 8,0 3 177977 50.056970395 0 C R 8726015 + 512 [0] > > : 8,0 3 177988 50.060326743 0 C R 8726527 + 512 [0] > > : 8,0 3 177999 50.063922341 0 C R 8727039 + 512 [0] > > : > > : after patch: > > : 8,0 3 257297 50.000760847 0 C R 9480703 + 256 [0] > > : 8,0 3 257306 50.003034240 0 C R 9480959 + 256 [0] > > : 8,0 3 257307 50.003076338 0 C R 9481215 + 256 [0] > > : 8,0 3 257323 50.004774693 0 C R 9481471 + 256 [0] > > : 8,0 3 257332 50.006865854 0 C R 9481727 + 256 [0] > > > > I haven't sent readahead-add-blk_run_backing_dev.patch in to Linus yet > and it's looking like 2.6.32 material, if ever. > > If it turns out to be wonderful, we could always ask the -stable > maintainers to put it in 2.6.x.y I guess. Agreed. The expected (and interesting) test on a properly configured HW RAID has not happened yet, hence the theory remains unsupported. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
