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    SubjectRe: filesystem benchmarking fun
    On Wed, 16 May 2007 16:14:14 -0400
    Chris Mason <chris.mason@oracle.com> wrote:

    > On Wed, May 16, 2007 at 01:04:13PM -0700, Andrew Morton wrote:
    > > > The good news is that if you let it run long enough, the times
    > > > stabilize. The bad news is:
    > > >
    > > > create dir kernel-86 222MB in 15.85 seconds (14.03 MB/s)
    > > > create dir kernel-87 222MB in 28.67 seconds (7.76 MB/s)
    > > > create dir kernel-88 222MB in 18.12 seconds (12.27 MB/s)
    > > > create dir kernel-89 222MB in 19.77 seconds (11.25 MB/s)
    > >
    > > well hang on. Doesn't this just mean that the first few runs were writing
    > > into pagecache and the later ones were blocking due to dirty-memory limits?
    > >
    > > Or do you have a sync in there?
    > >
    > There's no sync, but if you watch vmstat you can clearly see the log
    > flushes, even when the overall create times are 11MB/s. vmstat goes
    > 30MB/s -> 4MB/s or less, then back up to 30MB/s.

    How do you know that it is a log flush rather than, say, pdflush
    hitting the blockdev inode and doing a big seeky write?
    -
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