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I'm running a setup consisting of a Linux host OS and a Windows 7 guest (VMware Workstation). I'm trying to run 16 CPU-bound background jobs on the Linux host at nice values of 19 (the lowest possible priority; one for each virtual CPU) and simultaneously use the Windows VM as a normal desktop OS. For some reason the Linux background jobs make my Windows VM grind to a halt even though VMware's nice value is 0.

If it helps, I'm running an 8-core machine with hyperthreading, so 16 virtual CPUs. Since VMware Workstation only supports virtualizing 8 cores, only 8 of the cores are visible in the Windows guest.

Edit: The background jobs I'm running are almost purely CPU bound and perform virtually no I/O.

Edit # 2: It's not an issue with hyperthreading messing up scheduling. Disabling hyperthreading in the BIOS solves nothing.

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-20 is the highest priority, and don't forget you have a bunch of linux processes running in the background already, besides your jobs. –  Spencer Rathbun May 5 '11 at 19:55
    
@Spencer: Right, but AFAIK 0 is the highest priority for user processes. –  dsimcha May 5 '11 at 19:56
    
Another thing to look at would be if vmware uses a multiprocess architecture. That is, you have a central daemon process, and separate vm processes. I'm not familiar enough to know if that would be an issue. Or it could just be a settings issue in the vm setup. I know that I've run into that with virtual box. If you don't set it to allow 3d graphics acceleration, it runs like a dog with anything more than a feather weight graphical os, especially windows. –  Spencer Rathbun May 5 '11 at 20:02

2 Answers 2

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You can check whether it is really CPU or rather I/O that slowes your system. vmstat 1 might be a good idea, and maybe top. The 19 processes are supposed to do something, right?

Rememer that a desktop hdd can not take more than ~100 random I/Os per second. Nice'd processes should get less I/O, but so many of them will still get enough.

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I realized what was going on here. The jobs I was running were dumping a bunch of output I didn't care about to /dev/null. Running other jobs in the background that really are purely CPU bound works fine.

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