linux-kernel - Re: [patch] CFS scheduler, -v12

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Message-ID: <46561E67.3030207@bigpond.net.au>
Date:	Fri, 25 May 2007 09:23:19 +1000
From:	Peter Williams <pwil3058@...pond.net.au>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
CC:	Ingo Molnar <mingo@...e.hu>, colpatch@...ibm.com,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Con Kolivas <kernel@...ivas.org>,
	Christoph Lameter <clameter@....com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch] CFS scheduler, -v12

Siddha, Suresh B wrote:
> On Thu, May 24, 2007 at 12:43:58AM -0700, Peter Williams wrote:
>> Peter Williams wrote:
>>> The relevant code, find_busiest_group() and find_busiest_queue(), has a 
>>> lot of code that is ifdefed by CONFIG_SCHED_MC and CONFIG_SCHED_SMT and, 
>>> as these macros were defined in the kernels I was testing with, I built 
>>> a kernel with these macros undefined and reran my tests.  The 
>>> problems/anomalies were not present in 10 consecutive tests on this new 
>>> kernel.  Even better on the few occasions that a 3/1 split did occur it 
>>> was quickly corrected to 2/2 and top was reporting approx 49% of CPU for 
>>> all spinners throughout each of the ten tests.
>>>
>>> So all that is required now is an analysis of the code inside the ifdefs 
>>> to see why it is causing a problem.
>>
>> Further testing indicates that CONFIG_SCHED_MC is not implicated and
>> it's CONFIG_SCHED_SMT that's causing the problem.  This rules out the
>> code in find_busiest_group() as it is common to both macros.
>>
>> I think this makes the scheduling domain parameter values the most
>> likely cause of the problem.  I'm not very familiar with this code so 
>> I've added those who've modified this code in the last year or 
>> so to the 
>> address of this e-mail.
> 
> What platform is this? I remember you mentioned its a 2 cpu box. Is it
> dual core or dual package or one with HT?

It's a single CPU HT box i.e. 2 virtual CPUs.  "cat /proc/cpuinfo" produces:

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 3
model name      : Intel(R) Pentium(R) 4 CPU 3.20GHz
stepping        : 4
cpu MHz         : 3201.145
cache size      : 1024 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 1
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge 
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe 
constant_tsc pni monitor ds_cpl cid xtpr
bogomips        : 6403.97
clflush size    : 64

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 15
model           : 3
model name      : Intel(R) Pentium(R) 4 CPU 3.20GHz
stepping        : 4
cpu MHz         : 3201.145
cache size      : 1024 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 1
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge 
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe 
constant_tsc pni monitor ds_cpl cid xtpr
bogomips        : 6400.92
clflush size    : 64


Peter
-- 
Peter Williams                                   pwil3058@...pond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce
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