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    <p>From <a href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.paralleloptions.maxdegreeofparallelism(v=vs.110).aspx" rel="noreferrer">http://msdn.microsoft.com/en-us/library/system.threading.tasks.paralleloptions.maxdegreeofparallelism(v=vs.110).aspx</a></p> <blockquote> <p>By default, <a href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.parallel.for(v=vs.110).aspx" rel="noreferrer"><code>For</code></a> and <a href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.parallel.foreach(v=vs.110).aspx" rel="noreferrer"><code>ForEach</code></a> will utilize however many threads the underlying scheduler provides. Changing MaxDegreeOfParallelism from the default only limits how many concurrent tasks will be used.</p> </blockquote> <p>This means that setting <code>MaxDegreeOfParallelism</code> to the number of processors will in fact limit the capacity of the <code>Parallel.For</code> loop to use the optimal amount of threads for the work load. For example, I have a migration job that uses close to 60 threads on around 600 iterations of long-running code, a lot more than the <em>1 thread per processor</em> limit that you're trying to set.</p> <p><code>MaxDegreeOfParallelism</code> or <code>ThreadPool.SetMaxThreads</code> should only be used if you explicitly need to prevent more than a given number of threads from executing. For example, if using an Access database, I would set it to 64, because that's the maximum number of concurrent connections that can be handled by Access for a single process.</p>
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    1. POMaxDegreeOfParallelism = Environment.ProcessorCount slows down execution time on my CPU
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    1. USBenjamin Beaulieu
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    1. COGood answer. As mentioned, it is best to not set this explicitly unless you have a specific reason to do so.
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      1. USErik
    2. COI actually changed the value of MaxDegreeOfParallelism = ENvironment.ProcessorCount to MaxDegreeOfParallelism = 16 and saw that it ran faster. You see I'm trying to create a test tool that is used to test how long different CPUs perform a task and I want to have the same test for each CPu thats why I want to set a limit on the number of Threads.
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      1. USHarry Boy
    3. COCan someone please explain to me the following. If I set MaxDegreeOfParallelism = Environment.ProcessorCount (Which is 8) does that mean one thread is running on each processor so that means the task is truely being executed in parallel? And if I set MaxDegreeOfParallelism to be 16 then that would mean that there are 2 threads running on each processor, but that each of these two threads have to switch between each other so it not true parallel processing??
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