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JohnO356

Force Processor to Use all 4 Cores

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Has anyone seen/tried this?   I found it someplace the other day while searching for "FSX on an SSD"

 

What it says is start FSX, go to Task Manager, right click on FSX under Processes, then left click on Affinity where you will see all the boxes checked. Uncheck all but 1st core and click OK. Then go back to Affinity and recheck all boxes which will force FSX to use all 4 cores.

 

I've never heard of it, but decided to try it.  BUT, I don't have the "Affinity" option.  I'm using Win 7, Home, 64bitt.

 

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For a quad core processor, FSX will use all 4 cores by default.

 

Just start up Windows Task Manager, and look in the Performance tab, with FSX running.

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If however you had 8 cores and wanted to use just 4 for FSX, then you can set this in the Affinity Mask in the FSX config. 

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Has anyone seen/tried this?

 

Years ago, and if you add one single line to your FSX.cfg file all this can happen automatically each time you start FSX.

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The affinity mask can only be used to block the use of cores, or in HT mode they are called Logical Processors (LP). In HT mode each core is split into two LPs (HT supported processors only). These look like two cores to the system. Since sooner or later a core will be required to run other threads it will have to stop and save what it's doing and load up the other thread. HT enabled improves this performance, HT disabled causes inefficient thread swapping.

 

When we have HT enabled the FSX threads will line up on contiguous LPs, when we would prefer the main FSX thread to occupy it's own core. In this case we use an Affinity Mask to block off one of the LPs so the next thread moves onto the next core, leaving the main FSX thread to run on a core all on it's own.

 

Affinity masks also allow the engineer to control heat to a certain extent, especially when there are multiple CPUs.

 

The application is best started with an AM setting since using the Task Manager to set/unset cores or LPs won't necessarily get the application to align its threads the way we intended.

 

In FSX we put a new section in fsx.cfg so that the application starts up it's threads properly:

 

[JOBSCHEDULER]

AffinityMask=0

 

We would by default have an AM=0 if we do not include the JOBSCHEDULER section, this enables all cores or LPs.

 

With a 4 core HT enabled processor we have 8 LPs (on supported CPUs). We would want the first FSX thread to get a core of it's own so there is less thread switching, although this won't stop other apps using the LPs of that core.

 

We might use an AM=170 which in Binary is 10101010, the right most 0 represents the first LP of the first core. We use the Windows calculator in Programmer mode and switch between Dec and Bin. The right most pair "10" means that the first LP is disallowed use by the app, the second LP will load the first thread, the other threads will move on to find the next available LP. Windows sees the first core is utilised and finds another available core for the next LP.

 

In FSX we might only enable three cores (or LPs) to leave one free for windows to find for other apps threads.

 

AM=168 represents 10101000 which effectively disables the first core.

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