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    SubjectRe: [RESEND] [PATCH] readahead:add blk_run_backing_dev
    On Mon, Jul 13, 2009 at 08:47:31PM +0800, Ronald Moesbergen wrote:
    > 2009/7/13 Wu Fengguang <fengguang.wu@intel.com>:
    > > On Mon, Jul 13, 2009 at 08:12:14PM +0800, Ronald Moesbergen wrote:
    > >> 2009/7/10 Vladislav Bolkhovitin <vst@vlnb.net>:
    > >> >
    > >> > Vladislav Bolkhovitin, on 07/10/2009 12:43 PM wrote:
    > >> >>
    > >> >> Ronald Moesbergen, on 07/10/2009 10:32 AM wrote:
    > >> >>>>
    > >> >>>> I've also long ago noticed that reading data from block devices is
    > >> >>>> slower
    > >> >>>> than from files from mounted on those block devices file systems. Can
    > >> >>>> anybody explain it?
    > >> >>>>
    > >> >>>> Looks like this is strangeness #2 which we uncovered in our tests (the
    > >> >>>> first
    > >> >>>> one was earlier in this thread why the context RA doesn't work with
    > >> >>>> cooperative I/O threads as good as it should).
    > >> >>>>
    > >> >>>> Can you rerun the same 11 tests over a file on the file system, please?
    > >> >>>
    > >> >>> I'll see what I can do. Just te be sure: you want me to run
    > >> >>> blockdev-perftest on a file on the OCFS2 filesystem which is mounted
    > >> >>> on the client over iScsi, right?
    > >> >>
    > >> >> Yes, please.
    > >> >
    > >> > Forgot to mention that you should also configure your backend storage as a
    > >> > big file on a file system (preferably, XFS) too, not as direct device, like
    > >> > /dev/vg/db-master.
    > >>
    > >> Ok, here are the results:
    > >
    > > Ronald, thanks for the numbers!
    >
    > You're welcome.
    >
    > >> client kernel: 2.6.26-15lenny3 (debian)
    > >> server kernel: 2.6.29.5 with readahead patch
    > >
    > > Do you mean the context readahead patch?
    >
    > No, I meant the blk_run_backing_dev patch. The patchnames are
    > confusing, I'll be sure to clarify them from now on.

    That's OK. I did see previous benchmarks were not helped by context
    readahead noticeably on CFQ, hehe.

    Thanks,
    Fengguang


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