linux-kernel - Re: [PATCH v3 linux-next] cpufreq: ondemand: Calculate gradient of CPU load to early increase frequency

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Date:	Thu, 04 Apr 2013 02:30:32 +0300
From:	Stratos Karafotis <stratosk@...aphore.gr>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Viresh Kumar <viresh.kumar@...aro.org>, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 linux-next] cpufreq: ondemand: Calculate gradient of
 CPU load to early increase frequency

On 04/03/2013 02:14 PM, Rafael J. Wysocki wrote:
> On Wednesday, April 03, 2013 12:13:56 PM Viresh Kumar wrote:
>> On 3 April 2013 12:01, stratosk <stratosk@...aphore.gr> wrote:
>>> I'm sorry, I don't understand.
>>> The goal of this patch is not energy saving.
>>
>> He probably misunderstood it...
>>
>>> The goal is to detect CPU load as soon as possible to increase frequency.
>>>
>>> Could you please clarify this?
>>
>> But he is looking for some numbers to prove your patch. Some numbers
>> that shows performance is better with your changes...
> 
> Yes.  If the goal of the patch is to improve performance, it would be good to
> know that it does meet the goal. IOW, *something* is supposed to be better with
> the patch and if so, numbers in support of this should be provided.
> 
> Thanks,
> Rafael

I tried to do some measurements simulating a CPU load with a loop that simply counts
an integer. The first test simulates a CPU load that lasts 2 x sampling_rate = ~ 20000us.
The second ~40000us and the third ~60000us.
There are 5 runs in each test. In each run the benchmark program counts 20 times with
early_demand off and 20 times with early_demand on and takes the average times.

I run the benchmark program on 3.9-rc5 + early_demand patch. My CPU is the i7-3770 @ 3.40 GHz

Please find below the results, and the benchmark code attached.
Please note, that the idea of this patch is to push the CPU to max frequency few sampling
periods (1 in most cases) earlier for a more responsive system. 

Thanks for your time,
Stratos

--------

counter 10,000,000
run	early_demand off	early_demand on		diff
1	20183us			20100us			0.41%
2	20127us			20091us			0.18%
3	20121us			20034us			0.43%
4	20262us			20043us			1.08%
5	20192us			20101us			0.45%

counter 20,000,000
run	early_demand off	early_demand on		diff
1	40037us			39846us			0.47%
2	40051us			39829us			0.55%
3	39996us			39845us			0.38%
4	40104us			39876us			0.57%
5	40090us			39841us			0.62%

counter 30,000,000
run	early_demand off	early_demand on		diff
1	60010us			59834us			0.29%
2	59560us			59854us			-0.491%
3	60006us			59827us			0.29%
4	59998us			59828us			0.28%
5	60012us			59866us			0.24%


View attachment "bench.c" of type "text/x-csrc" (1944 bytes)