Messages in this thread Patch in this message | | | Subject | Re: iozone regression with 2.6.29-rc6 | From | Lin Ming <> | Date | Mon, 02 Mar 2009 10:19:04 +0800 |
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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%)
Lin Ming
> > --- > Subject: mm: bdi: tweak task dirty penalty > From: Peter Zijlstra <a.p.zijlstra@chello.nl> > Date: Fri Feb 27 10:41:22 CET 2009 > > Penalizing heavy dirtiers with 1/8-th the total dirty limit might be rather > excessive on large memory machines. Use sqrt to scale it sub-linearly. > > Update the comment while we're there. > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > --- > mm/page-writeback.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > Index: linux-2.6/mm/page-writeback.c > =================================================================== > --- linux-2.6.orig/mm/page-writeback.c > +++ linux-2.6/mm/page-writeback.c > @@ -293,17 +293,21 @@ static inline void task_dirties_fraction > } > > /* > - * scale the dirty limit > + * Task specific dirty limit: > * > - * task specific dirty limit: > + * dirty -= 8 * sqrt(dirty) * p_{t} > * > - * dirty -= (dirty/8) * p_{t} > + * Penalize tasks that dirty a lot of pages by lowering their dirty limit. This > + * avoids infrequent dirtiers from getting stuck in this other guys dirty > + * pages. > + * > + * Use a sub-linear function to scale the penalty, we only need a little room. > */ > static void task_dirty_limit(struct task_struct *tsk, long *pdirty) > { > long numerator, denominator; > long dirty = *pdirty; > - u64 inv = dirty >> 3; > + u64 inv = 8*int_sqrt(dirty); > > task_dirties_fraction(tsk, &numerator, &denominator); > inv *= numerator; > >
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