Messages in this thread | | | Date | Sat, 20 Jun 2009 16:29:31 +0400 | From | Vladislav Bolkhovitin <> | Subject | Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev |
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Wu Fengguang, on 06/20/2009 07:55 AM wrote: > 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@intel.com> 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.
Hmm, do you see anything improper in the Ronald's setup (see http://sourceforge.net/mailarchive/forum.php?thread_name=a0272b440906030714g67eabc5k8f847fb1e538cc62%40mail.gmail.com&forum_name=scst-devel)? It is HW RAID based.
As I already wrote, we can ask Ronald to perform any needed tests.
> Thanks, > Fengguang
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