Bitsum developed ParkControl because core parking settings are hidden in Windows, but can make such a large difference on performance, particularly when there are bursting CPU bound loads (the most common type).
Benchmark results and images courtesy of XTremeHardware.
Core Parking is a sleep state (C6) supported by most newer x86 processors, and newer editions of Windows. Core Parking dynamically disables CPU cores in an effort to conserve power when idle. Disabled cores are re-enabled as the CPU load increases once again. This technology is very similar to frequency scaling, in that it seeks to throttle the CPU when idle.
The problem is that Window’s default power profiles are configured far too aggressively when it comes to core parking, especially on workstations. Their interest was in conserving energy, even if this meant marginally decreasing performance. A number of complex parameters control when a core should be parked, and Microsoft tuned heavily towards power savings.
The core parking settings in Windows are implemented as parameters of power plans (aka power profiles). That means you can, for example, disable core parking for the High Performance power plan, but leave it enabled for other plans. And that is exactly the desired tweak for most users: disable parking only for high performance power plans.
Empirical evidence shows that disabling core parking can make a real difference in system performance. There are many factors that will determine how efficacious it will be for any given system, including the CPU type, application load, and user behavior. However, we find that Windows is often over-aggressive in its core parking, resulting in excess latency as cores are unparked to accommodate bursting loads (the most common type of CPU load).
In our tests, we’ve found AMD processors benefit most from disabling core parking. This is perhaps due to the dramatic difference in the way AMD processors share (hardware) computational resources between logical cores. Microsoft optimized for Intel’s HyperThreading, which has much less capable secondary cores. AMD’s secondary logical cores are near full CPUs.
YMMV, but if we didn’t see real and substantial performance gains after disabling core parking, we wouldn’t have authored this utility.
These tweaks are entirely safe for any PC that is constructed properly. The only way that they could possibly seem to cause some change in behavior is if the PC has overheating issues. In such an event, those issues would be seen regardless of these tweaks by simply placing a sustained high load on the CPU.
- Click ‘Power Options’ in the ParkControl app
- Select the Power Profile you modified
- Click ‘Restore default settings for this plan’
- Repeat for all modified power plans
Changing Parking Settings Using ParkControl
Simply run ParkControl, select the target power profile, change the setting, and click apply!
What is that NUMBER that is shown on the GUI? That is the % of cores that must remain *unparked*. So, if it’s 25%, then 75% of the CPU’s cores can be parked at once (3 of 4).
Changing Parking Settings Using PowerCfg.exe
Here at Bitsum, we won’t force you to use our software. We’ll tell you how to do it yourself, the *right* way, unlike many other web sites.
Getting to business, you can change these settings yourself via Window’s Powercfg.exe. You must run this utility with elevated rights, so be sure to open an elevated console window by right-clicking ‘cmd.exe’ and selecting ‘Run as Administrator’ (now in the ‘More’ submenu in the latest Windows 10 update).
Also note that these commands adjust the current power profile. I felt it simplest to use these variables as opposed to giving you GUIDs that may or may not apply to your PC’s power profile setup.
FIRST, Backup ALL your Power Settings by creating a dump of everything to a TXT file. You can later use this to revert to your default settings.
powercfg /qh > powerconfig.txt
To mandate 50% of available cores always remain unparked, run:
powercfg -setacvalueindex scheme_current sub_processor 0cc5b647-c1df-4637-891a-dec35c318583 50
To adjust it so that only 25% of available cores remain active at all times, allowing 75% of available cores to be parked, you’d run:
powercfg -setacvalueindex scheme_current sub_processor 0cc5b647-c1df-4637-891a-dec35c318583 25
Yes, you can use ‘0’ – Windows is not stupid enough to park all cores at once, it will always leave at least one core active. In fact, this is usually the default setting when it is enabled. For example, to enable maximum use of CPU Parking for the power profile you are *currently* using:
powercfg -setacvalueindex scheme_current sub_processor 0cc5b647-c1df-4637-891a-dec35c318583 0
To disable CPU Parking completely for the power profile you are *currently* using, you’d want to run:
powercfg -setacvalueindex scheme_current sub_processor 0cc5b647-c1df-4637-891a-dec35c318583 100
APPLY New Settings, NOW!
After changing the power scheme settings for CPU Parking as desired, you then want to make the changes active by running the command:
powercfg -setactive scheme_current
When I first wrote this I included allowing specification of AC or DC (battery) values for the power scheme. Setting the DC power value isn’t documented, so I am going to skip that. Still, to do so you’d simply replace ‘-setacvalueindex’ with ‘-setdcvalueindex’. It also is not entirely clear if this is supported for every power scheme, though it certainly appears to be. Sadly, Microsoft’s documentation is quite scarce.
You should not have to reboot for these changes to take effect. They are immediate! Go ahead and check the Resource Monitor and verify that CPU Parking is indeed as you set it.
I hope this helps some people. Why would you go around making manual edits to the registry when powercfg can do the job for you? You shouldn’t. Registry edits are prone to mistakes and are generally more tedious and less clear.
How to Show Core Parking Options in the Advanced Power Options
Too bad this option is NOT shown by default in the Windows Power Options, eh? Well, it can be! You can make your Advanced Power Options in Windows show this value!
Download the .REG file here (you can use the freeware RegMerge to see what is inside before applying): DOWNLOAD REG TWEAK
The actual REG file contents are below.
Windows Registry Editor Version 5.00
We’ve attempted to dig deeper into the core parking rabbit hole, and let me tell you there are countless additional hidden variables that control it’s behavior. It’s therefore not at all inconceivable that some are not tuned properly. In fact, Microsoft has issued Hotfixes in the past to address this very issue.
I’ll update my findings here as I’m able. If you want to support this project, buy a license for Process Lasso or donate.
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