1.    19 Jun 2017 #1
    Join Date : Sep 2016
    Posts : 17
    windows 10 home

    How can I exclude a core from scheduling any threads?


    I have an AMD A10-7850K (Steamroller). This CPU has cores arranged in pairs which share certain resources.
    I want to do timing tests on a program (call it X), where it runs exclusively on one core (say, 2), while nothing runs at all on its partner core (in this case, core 3). (This is on a CPU with 4 cores enabled.)
    I know how to do the first part, by setting X's affinity to core 2 and realtime priority so that Windows will never interrupt it on core 2.
    But I don't know how to keep core 3 "parked".

    My motherboard allows me to set the number of pairs of cores that are visible to Windows. I'd like to enable 3 cores, and then pin X to core 2, but that doesn't seem to be possible with the BIOS.

    I have 4 cores on my machine (currently set in the BIOS). I notice that Windows seems to park or unpark cores 2 and 3 at the same time, and never unparks core 0 or 1.

    I can think of a some possibilities.

    1. Come up with a program (Y) to pin to core 1 which runs at realtime priority but doesn't consume any resources, such as by running a halt instruction or waiting for some event that will never happen. However, I don't know if Windows will schedule some other thread for core 1 when Y is in a wait state.

    2. Is there something in the Registry which will park a specific core? This might be done separately for each power plan.

    3. Is there something in the Registry that would set the min number of unparked cores? I know I can set the max % to a low number in order to disable parking altogether. If I can set the min to, say 50%, I would guess that cores 2 and 3 will always be parked. If I pin X to core 2 (assuming that Windows will use a parked core to satisfy the affinity of X), then core 3 should remain unscheduled. If Windows will not use a parked core for X, then I would want to set the min to 75% to unpark 0, 1, and 2 while 3 is parked.

    4. If all else fails, I'll just leave the system as it is, and shut down as many processes as I can, and hope that core 3 won't get used very much. My timing tests should be valid for brief intervals of time and I can infer that speed of X when running without interference from core 3. I've seen that if I have X pinned to core 2, then Windows tends to schedule other work evenly among cores 0, 1, and 2.
      My ComputerSystem Spec
  2.    20 Jun 2017 #2
    Join Date : Jan 2015
    UK, Midlands
    Posts : 11,079
    Win 10 Pro (1703)

    Hi, this is probably not what you're looking for- not an area I've looked into- but here it is anyway- it can't be as simple as this:
    Click image for larger version. 

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ID:	140308
      My ComputerSystem Spec

 


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