Tune up Windows: Processors

Windows 7 adds support for several new CPU features that reduce energy use, which sounds great – except some say they compromise performance. Worse, all these settings are hidden by default, however that can be changed.

Enter the following two commands at the command prompt: powercfg -attributes SUB_PROCESSOR 0cc5b647-c1df-4637-891a-dec35c318583-ATTRIB_HIDE and powercfg-attributes SUB_PROCESSOR ea062031-0e34-4ff1-9b6deb1059334028-ATTRIB_HIDE. Now go to ‘Control Panel | Power options | Change plan settings (for your current plan) | Change advanced power settings | Processor power management’. You’ll see two new options: ‘Processor performance core parking min cores’ and ‘Processor performance core parking max cores’.

These settings relate to Core Parking, a feature that allows your CPU to turn off some cores to save power when your system load is minimal. While generally a good thing, some say it causes problems, and recommend turning parking off. Set ‘Min cores’ and ‘Max cores’ to 100 and reboot your machine to make this happen.

Need more tweaks? There are plenty, including additional Core Parking options, performance management, idle states and more. Download Microsoft’s guide to Processor Power Management (www.bit.ly/duZ9ps) and locate a setting of interest. Copy its GUID from the document – ‘Allow throttle states’ is ‘3b04d4fd-1cc7-4f23-ab1c-d1337819c4bb’, for instance – and build a command along the lines of powercfg -attributes SUB_PROCESSOR 3b04d4fd-1cc7-4f23-ab1c-d1337819c4bb -ATTRIB_HIDE.

Enter this at the command line and the new setting will be visible. (Use +ATTRIB_HIDE at the end to hide it again.) Keep in mind that there’s a reason why many of these tweaks are hidden, though. If you disable PC idle states, for instance, you may gain a tiny amount in terms of performance, but your CPU could also run very hot, shortening its life. Change your settings carefully, ideally monitoring details like temperature for any changes.

Some CPU features are hidden by default and are only available if they’re turned on in the BIOS, so check here first.

CPU scheduling

PCs are always busy, with far more processes active then there are CPU cores available. Windows manages this by running each thread for a brief period, called a quantum. When that time is up, the scheduler looks for other apps that need the CPU and runs one of those. By default, this system triples the quantum for the foreground application, and generally does a good job of sharing processor time. But if you want to improve things, there are a couple of ways to do it.

One option is to use the Windows Server scheduling settings. These don’t optimise the foreground application, so your user interface won’t feel so snappy, but they provide a quantum six times longer than usual, minimising overheads and improving CPU efficiency.

To try this, right-click ‘Computer,’ click ‘Advanced’ (then ‘Performance settings | Advanced’ in Vista or later) and set ‘Adjust for best performance of’ to ‘Background services’. Or you can customise your quantum manually. Run ‘REGEDIT’, browse to ‘HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\PriorityControl’, set ‘Win32 PrioritySeparation’ to ‘16 (Hex)’, and you’ll get a long quantum that also optimises the foreground app – a good compromise.

Benchmarking

Windows Vista and 7 configure many CPU settings automatically when you select a power plan, so it’s important to choose it wisely. On our test system, opting for the ‘High performance’ power plan over the ‘Power saver’ increased our CPU speed by around 10 per cent, according to several speed tests.

How can you be sure that, say, disabling Core Parking has improved your system speeds? You need a decent benchmark tool, and SiSoft Sandra (www.sisoftware.co.uk) is the perfect example: comprehensive, packed with features yet easy to use, and free to try.

With a little help from SiSoft Sandra, you’ll be able to define your baseline system speed, then spot which tweaks improve performance, and which might be slowing you down.

1 Choose a test

Begin by downloading and installing the program from www.sisoftware.co.uk, accepting the default installation options for now. Click the ‘Benchmarks’ tab to see the available speed tests, and double-click whatever you’d like to check: ‘Processor Arithmetic’, for example.

2 Check the results

Click the toolbar’s ‘Refresh’ button to run the speed tests. Do this a couple of times, note the results, then apply your CPU tweak (or any other adjustment). It’s faster? Great. Slower? Oops. Run the test once more to be sure, and if there’s still no change, restore your default CPU settings.