linux-kernel - Re: [RFC PATCH 2/3] sched: power aware load balance,

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Date:	Wed, 07 Nov 2012 20:42:02 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	rob@...dley.net, mingo@...hat.com, peterz@...radead.org,
	suresh.b.siddha@...el.com, arjan@...ux.intel.com,
	vincent.guittot@...aro.org, tglx@...utronix.de,
	gregkh@...uxfoundation.org, andre.przywara@....com, rjw@...k.pl,
	paul.gortmaker@...driver.com, paulmck@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, cl@...ux.com, pjt@...gle.com
Subject: Re: [RFC PATCH 2/3] sched: power aware load balance,

On 11/07/2012 03:51 AM, Andrew Morton wrote:
> On Tue,  6 Nov 2012 21:09:58 +0800
> Alex Shi <alex.shi@...el.com> wrote:
> 
>> $for ((i=0; i < I; i++)) ; do while true; do : ; done & done
>>
>> Checking the power consuming with a powermeter on the NHM EP.
>> 	powersaving     performance
>> I = 2   148w            160w
>> I = 4   175w            181w
>> I = 8   207w            224w
>> I = 16  324w            324w
>>
>> On a SNB laptop(4 cores *HT)
>> 	powersaving     performance
>> I = 2   28w             35w
>> I = 4   38w             52w
>> I = 6   44w             54w
>> I = 8   56w             56w
>>
>> On the SNB EP machine, when I = 16, power saved more than 100 Watts.
> 
> Confused.  According to the above table, at I=16 the EP machine saved 0
> watts.  Typo in the data?

Not typo, since the LCPU number in the EP machine is 16, so if I = 16,
the powersaving policy doesn't work actually. That is the patch designed
for race to idle assumption.

The result looks same as the third patch(for fork/exec/wu) applied.
Result put here because it is from this patch.

> 
> 
> Also, that's a pretty narrow test - it's doing fork and exec at very
> high frequency and things such as task placement decisions at process
> startup might be affecting the results.  Also, the load will be quite
> kernel-intensive, as opposed to the more typical userspace-intensive
> loads.

Sorry, why you think it keep do fork/exec? It just generate several
'bash' task to burn CPU, without fork/exec.

with I = 8, on my 32 LCPU SNB EP machine:
No do_fork calling in 5 seconds.

$ sudo perf stat -e probe:* -a sleep 5
 Performance counter stats for 'sleep 5':
           3 probe:do_execve           [100.00%]
           0 probe:do_fork             [100.00%]

And it is not kernel-intensive, it nearly running all in user level.

'Top' output: 25:0%us VS 0.0%sy

Tasks: 319 total,   9 running, 310 sleeping,   0 stopped,   0 zombie
Cpu(s): 25.0%us,  0.0%sy,  0.0%ni, 74.5%id,  0.4%wa,  0.1%hi,  0.0%si,
0.0%st
...

> So, please run a broader set of tests so we can see the effects?
> 

Really, I have no more ideas for the suitable benchmarks.

Just tried the kbuild -j 16 on the 32 LCPU SNB EP, power just saved 10%,
but compile time increase about ~15%.
Seems if the task number is variation around the powersaving criteria
number, that just cause trouble.




-- 
Thanks
    Alex
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