Detecting the number of processors

Question

How do you detect the number of physical processors/cores in .net?

Teece

Answer 1

System.Environment.ProcessorCount

returns the number of logical processors

http://msdn.microsoft.com/en-us/library/system.environment.processorcount.aspx

For physical processor count you'd probably need to use WMI - the following metadata is supported in XP/Win2k3 upwards (Functionality enabled in SP's prior to Vista/Win2k8).

Win32_ComputerSystem.NumberOfProcessors returns physical count

Win32_ComputerSystem.NumberOfLogicalProcessors returns logical (duh!)

Be cautious that HyperThreaded CPUs appear identical to multicore'd CPU's yet the performance characteristics are very different.

To check for HT-enabled CPUs examine each instance of Win32_Processor and compare these two properties.

Win32_Processor.NumberOfLogicalProcessors

Win32_Processor.NumberOfCores

On multicore systems these are typically the same the value.

Also, be aware of systems that may have multiple Processor Groups, which is often seen on computers with a large number of processors. By default .Net will only using the first processor group - which means that by default, threads will utilize only CPUs from the first processor group, and Environment.ProcessorCount will return only the number of CPUs in this group. According to Alastair Maw's answer, this behavior can be changed by altering the app.config as follows:

<configuration>
   <runtime>
      <Thread_UseAllCpuGroups enabled="true"/>
      <GCCpuGroup enabled="true"/>
      <gcServer enabled="true"/>
   </runtime>
</configuration>

Despicable

You should note, it's supported only in XP SP3/Win2k3 and upwards. – Chatham

Answer 2

While Environment.ProcessorCount will indeed get you the number of virtual processors in the system, that may not be the number of processors available to your process. I whipped up a quick little static class/property to get exactly that:

using System;
using System.Diagnostics;

/// <summary>
/// Provides a single property which gets the number of processor threads
/// available to the currently executing process.
/// </summary>
internal static class ProcessInfo
{
    /// <summary>
    /// Gets the number of processors.
    /// </summary>
    /// <value>The number of processors.</value>
    internal static uint NumberOfProcessorThreads
    {
        get
        {
            uint processAffinityMask;

            using (var currentProcess = Process.GetCurrentProcess())
            {
                processAffinityMask = (uint)currentProcess.ProcessorAffinity;
            }

            const uint BitsPerByte = 8;
            var loop = BitsPerByte * sizeof(uint);
            uint result = 0;

            while (--loop > 0)
            {
                result += processAffinityMask & 1;
                processAffinityMask >>= 1;
            }

            return (result == 0) ? 1 : result;
        }
    }
}

Trellas

+1 for answering my question in a different post. #2135066 – Ferree

+1 not having all cores available can happen in quite a few scenarios, such as ASP.NET code in a "web-garden" configuration. – Spend

This does not answer the original question. ProcessorAffinity gets the "the processors on which the threads in this process can be scheduled to run," not the number of physical processors. On my Core i7, (4 cores w/ HT), ProcessorAffinity returns 255, which means 8 processors, which is not the number of physical processors. – Cohin

Answer 3

This actually varies quite a bit depending on the target platform. Stephbu's answer will work great on XP SP3 and newer.

If you are targeting older platforms, you may want to check out this article. I wrote it about half a year ago and in it I discuss several different ways to do this as well as the individual pros and cons of each method.

You may also want to check out this code project article if you are interested in differentiating shadow cores from hyperthreading from real ones.

Chatham

Hey Rick there was a HF for XP SP2 to support the same objects support.microsoft.com/kb/936235 – Despicable

Answer 4

System.Environment.ProcessorCount is what you need

Universe

posted Environment.GetEnvironmentVariable("NUMBER_OF_PROCESSORS") first, but then I realized it was already parsed in a separate property – Universe

ProcessorCount returns the number of logical processors, not the number of physical processors or even the number of cores. Not what the OP was asking. – Cohin

Answer 5

Environment.ProcessorCount

EDIT: available in .NET 2.0, not in .NET 1.1

Mecklenburg

Doesn't return the number of cores however. Only logical CPUs – Despicable

Answer 6

Environment.ProcessorCount will also include any hyperthreaded processors.

There is no way (at least up through Windows 2003) to distinguish a hyperthreaded processor from one with two cores.

Melisandra

Not quite true - there were several service packs to enable WMI CPU metadata for both XP and Win2k3 – Despicable

Fair enough -- when I needed to do it I was wanting to simply use the Win32 APIs not dig through WMI (especially if I had to know which processor had which features) – Melisandra

Answer 7

Don't have enough rep for the wiki, but note that in addition to XPSP2, Windows 2003 Server SP1 and SP2 also need a hotfix to enable this functionality:

http://support.microsoft.com/kb/932370

Carmine

Answer 8

You can use PowerShell to access comprehensive processor information. For example, you can run the following command to get the number of CPU cores:

Get-WmiObject -namespace root\CIMV2 -class Win32_Processor -Property NumberOfCores

It's much easier to research WMI when using some kind of explorer tool. So, I can suggest using WMI browsing tool (e.g. WMIExplorer or WMI CIM Studio) to explore WMI classes, properties and methods.

Wysocki