linux-kernel - Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28

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Date:	Wed, 17 Sep 2008 06:39:51 +0200
From:	Mike Galbraith <efault@....de>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-testers@...r.kernel.org
Subject: Re: [Bug #11308] tbench regression on each kernel release from
	2.6.22 -&gt; 2.6.28

On Tue, 2008-09-16 at 17:07 +0300, Ilpo Järvinen wrote:
> On Tue, 16 Sep 2008, Mike Galbraith wrote:
> 
> > On Mon, 2008-09-15 at 12:44 +0200, Mike Galbraith wrote:
> > > On Sun, 2008-09-14 at 21:51 +0200, Mike Galbraith wrote:
> > > 
> > > Since 2.6.22.19-cfs-v24.1 and 2.6.23.17-cfs-v24.1 schedulers are
> > > identical, and these are essentially identical with 2.6.24.7, what I
> > > read from numbers below is that cfs in 2.6.23 was somewhat less than
> > > wonderful for either netperf or tbench,  Something happened somewhere
> > > other than the scheduler at 23->24 which cost us some performance, and
> > > another something happened at 26->27.  I'll likely go looking again..
> > > and likely regret it again ;-)
> > 
> > Bisecting 26->27 yet again turned up a repeatable downturn in netperf
> > throughput.  There is no difference at this point with tbench. 
> > 
> > Bisect says first bad commit is 847106f, a security merge.  Post
> > bisection sanity checkouts say...
> > 
> > v2.6.26-21-g2069f45
> > 16384  87380  1        1       60.00    98435.13
> > 16384  87380  1        1       60.01    99259.90
> > 16384  87380  1        1       60.01    99325.61
> > 16384  87380  1        1       60.00    99039.84
> > 
> > v2.6.26-343-g847106f
> > 16384  87380  1        1       60.00    94764.59
> > 16384  87380  1        1       60.00    94909.89
> > 16384  87380  1        1       60.00    94858.63
> > 16384  87380  1        1       60.00    94801.12
> > 
> > ...every time.  I knew I'd regret doing this.
> 
> I assume that c142bda458a gave a good results as well...

Yes, just tried it.

> One additional sanity check could be to rebase security 6f0f0fd4963 on top 
> of the c142bda458a and then see if bisection among those security commits 
> on top yields to the the same result... Though I doubt it can change much 
> because there was not that much relevant non-security things in the merge 
> in question.

I'm not a master of git-foo, so that is not an option.  However, a dinky
bisection c142bda4..847106f very clearly says...

marge:..kernel/linux-2.6.27.git # git bisect bad
6f0f0fd496333777d53daff21a4e3b28c4d03a6d is first bad commit
commit 6f0f0fd496333777d53daff21a4e3b28c4d03a6d
Author: James Morris <jmorris@...ei.org>
Date:   Thu Jul 10 17:02:07 2008 +0900

    security: remove register_security hook

    The register security hook is no longer required, as the capability
    module is always registered.  LSMs wishing to stack capability as
    a secondary module should do so explicitly.

    Signed-off-by: James Morris <jmorris@...ei.org>
    Acked-by: Stephen Smalley <sds@...ho.nsa.gov>
    Acked-by: Greg Kroah-Hartman <gregkh@...e.de>

:040000 040000 0177ef46d305e51e27bfcc4350a40577f8ba8d3d 64b64c10a424df4539653a8ee34f1a2329300931 M      include
:040000 040000 e318891e514de674fd064f6bfad70d5633b1aff1 0dbb38d5aa7fc3e4b2e09dc65796ce7cd5faeb26 M      security

git bisect start
# good: [c142bda458a9c81097238800e1bd8eeeea09913d] Merge branch 'drm-reorg' of git://git.kernel.org/pub/scm/linux/kernel/git/airlied/drm-2.6
git bisect good c142bda458a9c81097238800e1bd8eeeea09913d
# bad: [847106ff628805e1a0aa91e7f53381f3fdfcd839] Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6
git bisect bad 847106ff628805e1a0aa91e7f53381f3fdfcd839
# good: [cea78dc4ca044e9666e8f5d797ec50ab85253e49] SELinux: fix off by 1 reference of class_to_string in context_struct_compute_av
git bisect good cea78dc4ca044e9666e8f5d797ec50ab85253e49
# good: [65fc7668006b537f7ae8451990c0ed9ec882544e] security: fix return of void-valued expressions
git bisect good 65fc7668006b537f7ae8451990c0ed9ec882544e
# good: [b478a9f9889c81e88077d1495daadee64c0af541] security: remove unused sb_get_mnt_opts hook
git bisect good b478a9f9889c81e88077d1495daadee64c0af541
# good: [93cbace7a058bce7f99319ef6ceff4b78cf45051] security: remove dummy module fix
git bisect good 93cbace7a058bce7f99319ef6ceff4b78cf45051
# bad: [6f0f0fd496333777d53daff21a4e3b28c4d03a6d] security: remove register_security hook
git bisect bad 6f0f0fd496333777d53daff21a4e3b28c4d03a6d


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