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    SubjectRe: iozone regression with 2.6.29-rc6
    On Mon, Mar 02, 2009 at 10:19:04AM +0800, Lin, Ming wrote:
    > On Fri, 2009-02-27 at 17:49 +0800, Peter Zijlstra wrote:
    > > On Fri, 2009-02-27 at 17:13 +0800, Lin Ming wrote:
    > > > bisect locates below commits,
    > > >
    > > > commit 1cf6e7d83bf334cc5916137862c920a97aabc018
    > > > Author: Nick Piggin <npiggin@suse.de>
    > > > Date: Wed Feb 18 14:48:18 2009 -0800
    > > >
    > > > mm: task dirty accounting fix
    > > >
    > > > YAMAMOTO-san noticed that task_dirty_inc doesn't seem to be called properly for
    > > > cases where set_page_dirty is not used to dirty a page (eg. mark_buffer_dirty).
    > > >
    > > > Additionally, there is some inconsistency about when task_dirty_inc is
    > > > called. It is used for dirty balancing, however it even gets called for
    > > > __set_page_dirty_no_writeback.
    > > >
    > > > So rather than increment it in a set_page_dirty wrapper, move it down to
    > > > exactly where the dirty page accounting stats are incremented.
    > > >
    > > > Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
    > > > Signed-off-by: Nick Piggin <npiggin@suse.de>
    > > > Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > > > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    > > > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    > > >
    > > >
    > > > below data in parenthesis is the result after above commit reverted, for example,
    > > > -10% (+2%) means,
    > > > iozone has ~10% regression with 2.6.29-rc6 compared with 2.6.29-rc5.
    > > > and
    > > > iozone has ~2% improvement with 2.6.29-rc6-revert-1cf6e7d compared with 2.6.29-rc5.
    > > >
    > > >
    > > > 4P dual-core HT 2P qual-core 2P qual-core HT
    > > > tulsa stockley Nehalem
    > > > --------------------------------------------------------
    > > > iozone-rewrite -10% (+2%) -8% (0%) -10% (-7%)
    > > > iozone-rand-write -50% (0%) -20% (+10%)
    > > > iozone-read -13% (0%)
    > > > iozone-write -28% (-1%)
    > > > iozone-reread -5% (-1%)
    > > > iozone-mmap-read -7% (+2%)
    > > > iozone-mmap-reread -7% (+2%)
    > > > iozone-mmap-rand-read -7% (+3%)
    > > > iozone-mmap-rand-write -5% (0%)
    > >
    > > Ugh, that's unexpected..
    > >
    > > So 'better' accounting leads to worse performance, which would indicate
    > > we throttle more.
    > >
    > > I take it you machine has gobs of memory.
    > >
    > > Does something like the below help any?
    >
    > It helps some as below test result,
    > The data in second parenthesis means 2.6.29-rc6-with-peter's-patch
    > compared with 2.6.29-rc5.
    >
    > 4P dual-core HT 2P qual-core 2P qual-core HT
    > tulsa stockley Nehalem
    > --------------------------------------------------------
    > iozone-rewrite -10% (+2%)(-3%) -8% (0%)(0%) -10% (-7%)(-2%)
    > iozone-rand-write -50% (0%)(-10%) -20% (+10%)(+3%)
    > iozone-read -13% (0%)(-8%)
    > iozone-write -28% (-1%)(+35%)
    > iozone-reread -5% (-1%)(-1%)
    > iozone-mmap-read -7% (+2%)(-7%)
    > iozone-mmap-reread -7% (+2%)(-7%)
    > iozone-mmap-rand-read -7% (+3%)(-7%)
    > iozone-mmap-rand-write -5% (0%)(+27%)

    Thanks, Lin Ming. To better understand the situation, would you please
    provide the iozone command and memory info about the servers?

    Thanks,
    Fengguang


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