linux-kernel - Re: VolanoMark regression with 2.6.27-rc1

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Date:	Tue, 06 Aug 2030 11:26:09 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Aneesh Kumar KV <aneesh.kumar@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ibm.com>
Subject: Re: VolanoMark regression with 2.6.27-rc1


On Mon, 2008-08-04 at 09:12 +0200, Peter Zijlstra wrote:
> On Mon, 2008-08-04 at 12:35 +0530, Dhaval Giani wrote:
> > On Mon, Aug 04, 2008 at 08:26:11AM +0200, Peter Zijlstra wrote:
> > > On Mon, 2008-08-04 at 11:23 +0530, Dhaval Giani wrote:
> > > 
> > > > Peter, vatsa, any ideas?
> > > 
> > > ---
> > > 
> > > Revert:
> > >   a7be37ac8e1565e00880531f4e2aff421a21c803  sched: revert the revert of: weight calculations
> > >   c9c294a630e28eec5f2865f028ecfc58d45c0a5a  sched: fix calc_delta_asym()
> > >   ced8aa16e1db55c33c507174c1b1f9e107445865  sched: fix calc_delta_asym, #2
> > > 
> > 
> > Did we not fix those? :) 
> 
> Works for me,.. just guessing here.
I did more investigation on 16-core tigerton.

Firstly, let's focus on CONFIG_GROUP_SCHED=n. With 2.6.26, the result has little difference
between with and without CONFIG_GROUP_SCHED.

1) I tried different sched_features and found AFFINE_WAKEUPS has big impact on volanoMark. Other
features have little impact.

2) With kernel 2.6.26, if disabling AFFINE_WAKEUPS, the result is 260000; if enabling AFFINE_WAKEUPS,
the result is 515000, so the improvement caused by AFFINE_WAKEUPS is about 100%. With kernel 2.6.27-rc1,
the improvement is only about 25%.

3) I turned on CONFIG_SCHETSTATS in kernel and collect ttwu_move_affine. Mostly, collect ttwu_move_affine,
then recollect it after 30 seconds and calculate the difference. With 2.6.26, I got below data:
domain0 279521 142332 0
domain1 184589 22823 0
domain0 289170 142168 0
domain1 185491 23778 0
domain0 291842 139687 0
domain1 187807 23174 0
domain0 292426 144879 0
domain1 179721 22122 0
domain0 287669 137756 0
domain1 201236 25156 0
domain0 268374 139532 0
domain1 210145 25268 0
domain0 292002 144530 0
domain1 196146 24669 0
domain0 298406 145023 0
domain1 178381 22743 0
domain0 275685 141086 0
domain1 203797 25686 0
domain0 285818 140260 0
domain1 180506 23002 0
domain0 290562 139757 0
domain1 186669 23086 0
domain0 296466 142084 0
domain1 186346 24161 0
domain0 283394 137930 0
domain1 195596 23895 0
domain0 269296 142978 0
domain1 210648 25682 0
domain0 281672 144002 0
domain1 189959 23685 0
domain0 301834 145922 0
domain1 172737 22351 0


The 3rd column is ttwu_move_affine difference.

With 2.6.27-rc1:
domain0 39054 302678 0
domain1 315384 245684 0
domain0 39142 304117 0
domain1 312896 244796 0
domain0 38636 304438 0
domain1 310687 244409 0
domain0 39534 304167 0
domain1 313746 245381 0
domain0 39082 304231 0
domain1 312592 245219 0
domain0 39057 305460 0
domain1 311395 245195 0
domain0 38224 301351 0
domain1 314482 244448 0
domain0 38016 300573 0
domain1 309031 241127 0
domain0 40285 306397 0
domain1 318707 243595 0
domain0 39685 305034 0
domain1 315380 241506 0
domain0 39828 306178 0
domain1 314515 243039 0
domain0 39870 303382 0
domain1 315457 244483 0
domain0 38892 304697 0
domain1 313808 241948 0
domain0 39255 303937 0
domain1 314531 244301 0
domain0 38850 300187 0
domain1 310727 240255 0
domain0 38847 302327 0
domain1 312538 241857 0


So with kernel 2.6.27-rc1, the successful wakeup_affine is about double of the one of 2.6.27-rc1
on domain 0, but about 10 times on domain 1. That means more tasks are woken up on waker cpus.

Does that mean it doesn't follow cache-hot checking?

I will collect more data.

-yanmin


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