Re: [PATCH v3 1/3] cpufreq: ondemand: Change the calculation of target frequency

[Rafael J. Wysocki]

On Friday, June 07, 2013 10:14:34 PM Stratos Karafotis wrote:
> On 06/05/2013 11:35 PM, Rafael J. Wysocki wrote:
> > On Wednesday, June 05, 2013 08:13:26 PM Stratos Karafotis wrote:
> >> Hi Borislav,
> >>
> >> On 06/05/2013 07:17 PM, Borislav Petkov wrote:
> >>> On Wed, Jun 05, 2013 at 07:01:25PM +0300, Stratos Karafotis wrote:
> >>>> Ondemand calculates load in terms of frequency and increases it only
> >>>> if the load_freq is greater than up_threshold multiplied by current
> >>>> or average frequency. This seems to produce oscillations of frequency
> >>>> between min and max because, for example, a relatively small load can
> >>>> easily saturate minimum frequency and lead the CPU to max. Then, the
> >>>> CPU will decrease back to min due to a small load_freq.
> >>>
> >>> Right, and I think this is how we want it, no?
> >>>
> >>> The thing is, the faster you finish your work, the faster you can become
> >>> idle and save power.
> >>
> >> This is exactly the goal of this patch. To use more efficiently middle
> >> frequencies to finish faster the work.
> >>
> >>> If you switch frequencies in a staircase-like manner, you're going to
> >>> take longer to finish, in certain cases, and burn more power while doing
> >>> so.
> >>
> >> This is not true with this patch. It switches to middle frequencies
> >> when the load < up_threshold.
> >> Now, ondemand does not increase freq. CPU runs in lowest freq till the
> >> load is greater than up_threshold.
> >>
> >>> Btw, racing to idle is also a good example for why you want boosting:
> >>> you want to go max out the core but stay within power limits so that you
> >>> can finish sooner.
> >>>
> >>>> This patch changes the calculation method of load and target frequency
> >>>> considering 2 points:
> >>>> - Load computation should be independent from current or average
> >>>> measured frequency. For example an absolute load 80% at 100MHz is not
> >>>> necessarily equivalent to 8% at 1000MHz in the next sampling interval.
> >>>> - Target frequency should be increased to any value of frequency table
> >>>> proportional to absolute load, instead to only the max. Thus:
> >>>>
> >>>> Target frequency = C * load
> >>>>
> >>>> where C = policy->cpuinfo.max_freq / 100
> >>>>
> >>>> Tested on Intel i7-3770 CPU @ 3.40GHz and on Quad core 1500MHz Krait.
> >>>> Phoronix benchmark of Linux Kernel Compilation 3.1 test shows an
> >>>> increase ~1.5% in performance. cpufreq_stats (time_in_state) shows
> >>>> that middle frequencies are used more, with this patch. Highest
> >>>> and lowest frequencies were used less by ~9%
> > 
> > Can you also use powertop to measure the percentage of time spent in idle
> > states for the same workload with and without your patchset?  Also, it would
> > be good to measure the total energy consumption somehow ...
> > 
> > Thanks,
> > Rafael
> 
> Hi Rafael,
> 
> I repeated the tests extracting also powertop results.
> Measurement steps with and without this patch:
> 1) Reboot system
> 2) Running twice Phoronix benchmark of Linux Kernel Compilation 3.1 test
>    without taking measurement
> 3) Wait few minutes
> 4) Run Phoronix and powertop for 100secs and take measurement.

Well, while this is not conclusive, it definitely looks very promising. :-)

We're seeing measurable performance improvement with the patchset applied *and*
more time spent in idle states both at the same time.  I'd be very surprised if
the energy consumption measuremets did not confirm that the patchset allowed
us to reduce it.

If my computations are correct (somebody please check), the cores spent about
20% more time in idle on the average with the patchset applied and in addition
to that the cc6 residency was greater by about 2% on the average with respect
to the kernel without the patchset.

We need to verify if there are gains (or at least no regressions) with other
workloads, but since this *also* reduces code complexity quite a bit, I'm
seriously considering taking it.

> I will try to repeat the test and take measurements with turbostat as
> Borislav suggested.

Please do!

Thanks,
Rafael


> ------------------------------------------------------------------
> Test WITHOUT this patch:
> 
> Phoronix Test Suite v4.6.0
> 
>     Installed: pts/build-linux-kernel-1.3.0
> 
> System Information
> 
> Hardware:
> Processor: Intel Core i7-3770 @ 3.40GHz (8 Cores), Motherboard: ASUS CM6870, Chipset: Intel Xeon E3-1200 v2/3rd, Memory: 2 x 4096 MB DDR3-1600MHz HY64C1C1624ZY, Disk: 1000GB Seagate ST1000DM003-9YN1, Graphics: NVIDIA GeForce GT 640 3072MB, Audio: Realtek ALC892, Monitor: S23B350, Network: Realtek RTL8111/8168 + Ralink RT3090 Wireless 802.11n 1T/1R
> 
> Software:
> OS: Fedora 18, Kernel: 3.10.0-rc3v+ (x86_64), Desktop: KDE 4.10.3, Display Server: X Server 1.13.3, Display Driver: nouveau 1.0.7, File-System: ext4, Screen Resolution: 1920x1080
> 
>     Would you like to save these test results (Y/n): n
> 
> 
> Timed Linux Kernel Compilation 3.1:
>     pts/build-linux-kernel-1.3.0
>     Test 1 of 1
>     Estimated Trial Run Count:    3
>     Estimated Time To Completion: 2 Minutes
>         Running Pre-Test Script @ 21:41:19
>         Started Run 1 @ 21:41:30
>         Running Interim Test Script @ 21:41:44
>         Started Run 2 @ 21:41:47
>         Running Interim Test Script @ 21:42:02
>         Started Run 3 @ 21:42:05
>         Running Interim Test Script @ 21:42:15  [Std. Dev: 19.28%]
>         Started Run 4 @ 21:42:19
>         Running Interim Test Script @ 21:42:29  [Std. Dev: 18.72%]
>         Started Run 5 @ 21:42:32
>         Running Interim Test Script @ 21:42:42  [Std. Dev: 17.84%]
>         Started Run 6 @ 21:42:46  [Std. Dev: 16.91%]
>         Running Post-Test Script @ 21:42:55
> 
>     Test Results:
>         11.073544979095
>         14.059958934784
>         9.6814110279083
>         9.6158590316772
>         9.5762379169464
>         9.5944919586182
> 
>     Average: 10.60 Seconds
> 
> Powertop results:
> http://www.semaphore.gr/results/powertop_without.html
> 
> 
> ---------------------------------------------------------------------
> Test WITH this patch:
> 
> Phoronix Test Suite v4.6.0
> 
>     Installed: pts/build-linux-kernel-1.3.0
> 
> System Information
> 
> Hardware:
> Processor: Intel Core i7-3770 @ 3.40GHz (8 Cores), Motherboard: ASUS CM6870, Chipset: Intel Xeon E3-1200 v2/3rd, Memory: 2 x 4096 MB DDR3-1600MHz HY64C1C1624ZY, Disk: 1000GB Seagate ST1000DM003-9YN1, Graphics: NVIDIA GeForce GT 640 3072MB, Audio: Realtek ALC892, Monitor: S23B350, Network: Realtek RTL8111/8168 + Ralink RT3090 Wireless 802.11n 1T/1R
> 
> Software:
> OS: Fedora 18, Kernel: 3.10.0-rc3+ (x86_64), Desktop: KDE 4.10.3, Display Server: X Server 1.13.3, Display Driver: nouveau 1.0.7, File-System: ext4, Screen Resolution: 1920x1080
> 
>     Would you like to save these test results (Y/n): n
> 
> 
> Timed Linux Kernel Compilation 3.1:
>     pts/build-linux-kernel-1.3.0
>     Test 1 of 1
>     Estimated Trial Run Count:    3
>     Estimated Time To Completion: 2 Minutes
>         Running Pre-Test Script @ 21:28:05
>         Started Run 1 @ 21:28:17
>         Running Interim Test Script @ 21:28:30
>         Started Run 2 @ 21:28:34
>         Running Interim Test Script @ 21:28:44
>         Started Run 3 @ 21:28:47
>         Running Interim Test Script @ 21:28:58  [Std. Dev: 4.81%]
>         Started Run 4 @ 21:29:02
>         Running Interim Test Script @ 21:29:12  [Std. Dev: 6.05%]
>         Started Run 5 @ 21:29:15
>         Running Interim Test Script @ 21:29:25  [Std. Dev: 6.13%]
>         Started Run 6 @ 21:29:28  [Std. Dev: 6.02%]
>         Running Post-Test Script @ 21:29:38
> 
>     Test Results:
>         10.442322015762
>         10.038927078247
>         11.044027090073
>         9.5781810283661
>         9.5812470912933
>         9.5545389652252
> 
>     Average: 10.04 Seconds
> 
> Powertop results:
> http://www.semaphore.gr/results/powertop_with.html
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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