linux-kernel - Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"

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Message-ID: <20110520234923.GQ2366@linux.vnet.ibm.com>
Date:	Fri, 20 May 2011 16:49:23 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	tglx@...utronix.de, mingo@...e.hu,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage
 based on semi-formal proof"

On Fri, May 20, 2011 at 04:16:28PM -0700, Yinghai Lu wrote:
> On 05/20/2011 04:14 PM, Paul E. McKenney wrote:
> > On Fri, May 20, 2011 at 04:09:22PM -0700, Yinghai Lu wrote:
> >> On 05/20/2011 03:42 PM, Paul E. McKenney wrote:
> >>> On Fri, May 20, 2011 at 02:04:06PM -0700, Yinghai Lu wrote:
> >>>> On 05/19/2011 02:37 PM, tip-bot for Paul E. McKenney wrote:
> >>>>> Commit-ID:  80d02085d99039b3b7f3a73c8896226b0cb1ba07
> >>>>> Gitweb:     http://git.kernel.org/tip/80d02085d99039b3b7f3a73c8896226b0cb1ba07
> >>>>> Author:     Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> >>>>> AuthorDate: Thu, 12 May 2011 01:08:07 -0700
> >>>>> Committer:  Ingo Molnar <mingo@...e.hu>
> >>>>> CommitDate: Thu, 19 May 2011 23:25:29 +0200
> >>>>>
> >>>>> Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"
> >>>>>
> >>>>> This reverts commit e59fb3120becfb36b22ddb8bd27d065d3cdca499.
> >>>>>
> >>>>> This reversion was due to (extreme) boot-time slowdowns on SPARC seen by
> >>>>> Yinghai Lu and on x86 by Ingo
> >>>>> .
> >>>>> This is a non-trivial reversion due to intervening commits.
> >>>>>
> >>>>> Conflicts:
> >>>>>
> >>>>> 	Documentation/RCU/trace.txt
> >>>>> 	kernel/rcutree.c
> >>>>>
> >>>>> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> >>>>> ---
> >>>>>  Documentation/RCU/trace.txt |   17 ++++--
> >>>>>  kernel/rcutree.c            |  130 ++++++++++++++++++++++++------------------
> >>>>>  kernel/rcutree.h            |    9 ++-
> >>>>>  kernel/rcutree_plugin.h     |    7 +-
> >>>>>  kernel/rcutree_trace.c      |   12 ++--
> >>>>>  5 files changed, 102 insertions(+), 73 deletions(-)
> >>>>>
> >>>>
> >>>> current tip/master that have this reverting and without setting DEBUG_LOCKING_API_SELFTESTS
> >>>>
> >>>> still get delay
> >>>>
> >>>> [   35.419453] cpu_dev_init done
> >>>> [  128.981770] memory_dev_init done
> >>>>
> >>>> should take only 3 or 4 seconds.
> >>>
> >>> Thank you for checking this out.
> >>>
> >>> This is with the same configuration you sent earlier?  (Other than the
> >>> DEBUG_LOCKING_API_SELFTESTS, of course.)
> >>>
> >>
> >> 8 socket westmere-ex. and compiled with gcc from opensuse 11.3.
> >>
> >> if compile kernel from fedora 14, there will be not delay.
> > 
> > Thank you for the info.  Could you please send me the .config files from
> > both builds?
> 
> the same one i sent out before, but let DEBUG_LOCKING_API_SELFTESTS disabled.

OK, just to make sure I understand...  You are compiling exactly the
same kernel source tree with exactly the same .config, just with two
different versions of gcc, correct?

If so, it is quite possible that the slow one is the correct one.  :-/

							Thanx, Paul
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