Poor performance with 2+ VMs open?

Discussion in 'Parallels Desktop for Mac' started by xochi, Nov 9, 2006.

  1. xochi

    xochi

    Messages:
    88
    I'm convinced there is some sort of performance problem with Parallels -- my hunch is that it has something to do with virtual memory swapping, though it might also be something to do with disk access.

    I've been seeing this with builds 1940 thru 1970. The basic issue is that when I open 2 or more VMs, my mac starts working really slowly. For example, if I switch from one VM to the finder, I get a beachball. Switch back to Safari, get another beachball. Back to finder -- beachball. This behavior is consistent with my mac being low on memory. However, this mac has 2 gigs of RAM, and I can verify (using Activity Monitor) that Parallels is not using over 600MB. Note that for both VMs, I have the Cache policy set to "Favor OSX".

    Other clues :
    Launch one VM, and boot windows XP. Play a song in iTunes. Go back to parallels and choose "New Window". Watch the second copy of Parallels launch. On my system, it takes 15-20 "dock bounces" to open! Also, the iTunes auido playback will stutter.

    Choose "New Window" to open a 3rd VM, and the same thing happens -- it takes nearly 30 seconds to open a new, untitled VM window.

    I think there is some problem with managing multiple active VMs -- anyone else agree?
     
  2. BlueSkyISdotCOM

    BlueSkyISdotCOM Bit Poster

    Messages:
    68
    How much RAM are you giving Parallels? (Preferences..., Memory tab)

    How much RAM are you giving each VM? (VM Configuration Editor)
     
  3. xochi

    xochi

    Messages:
    88
    Two VMs: Each with 300MB. Parallels is told to use no more than 1000MB.
     
  4. BlueSkyISdotCOM

    BlueSkyISdotCOM Bit Poster

    Messages:
    68
    Imagine trying to run Windows XP on a real PC with only 300 MB of RAM. That's barely enough (maybe not even enough) for Windows XP alone, never mind any running applications. With only 300 MB, your VMs are doing what a real PC would do: endlessly paging data on and off the hard drive because there isn't enough RAM to hold the data. Whenever you switch from one VM to another or do anything in either of them, a bunch of data has to be written and/or read from hard drive and that is many times slower than RAM.

    Assign at least 512 MB to your VMs. If you're going to run two 512 MB VMs, you'll need to set Parallels to higher than 1000MB, since you'll need (roughly) 1012 MB for the VMs plus some more for Parallel's own use.
     
  5. xochi

    xochi

    Messages:
    88
    Not true -- I'm seeing the terrible performance even when both VMs are totally idle (e.g. no programs running, and zero % cpu is being used). Windows XP can boot and sit idle just fine with only 300MB.

    I've used nearly identical VMs before in Virtual PC (same size, same tasks, same RAM configuration), and am finding that Parallels simply has much worse performance in some cases -- to be specific, I'm finding that Parallels seems to break down when more than one VM is open, with the result that performance for other Mac OS X apps goes to crap.

    Since the core duo macbook is 2x faster (give or take) than the G4, I can't understand why this would be. Therefore, I'm going to stick with my guess that there is some sort of performance bug in Parallels. I'm wondering if perhaps the "optimize for OSX" cache policy flag is not working? That's almost what it's looking like...
     
  6. Mr SA

    Mr SA

    Messages:
    46
    [Just a hunch mode]If you are using VT-X each virtual machine gets first dibs on an individual processor core. If you only have two processor cores, then two VMs will be hogging the processors.

    I get this problem on a Macpro (4x cores) with 4 x VMs. It even causes problems with the VMs open but not running.

    It is nothign to do with Windows. I get this with Linux livecds that happily run on 32MB, given 1000MB. The host machine has 10GB to play with.
     
  7. rjgebis

    rjgebis Kilo Poster

    Messages:
    186
    I see this all the time. I run usually two or three of them @ the same time (Linux, Soalris and Windows - First two (128 and 256Mb respectively ) in console mode and XP (640Mb). I have 1112 allocated for VM. I have all services turned off and I know nothing is running anything heavy. I have them for development. If I do not compile and machine is idle from user point of view I see Parallels working quite hard. when I do top in each os they all show idle.
     
  8. xochi

    xochi

    Messages:
    88
    In the recent past there was an application called PDTweaker http://www.multisolar.com/software/PDTweaker/ which remedied this problem. However, supposedly in build 1948 parallels fixed this. I wonder if, perhaps, they didn't fix this altogether?

    If so, then what is happening is that Parallels (or perhaps OSX) is trying to fill up RAM with a cached copy of the VM hard disk. This causes other OSX programs to be swapped out to the virtual memory pagefile, resulting in poor performance, even in situations where there should be plenty of RAM to go around?
     
  9. majortom

    majortom

    Messages:
    98
    Everything is fine for me with Win XP and Ubuntu Linux running together from 256MBytes each and up. Cacche policy better for Vm, of course. (2 Gbyte MacBook 2.0).
     
  10. Joe Mac User

    Joe Mac User

    Messages:
    10
    I've seen this too. I don't run multiple VMs often, so I can't say when it might have started, but I do recall that when I first got the first *release* of Parallels (never used any betas) it wasn't as bad as it is now. I'm not running anything else on this computer when I'm doing this, just Parallels.

    For me, it's two VMs each with XP, running on a Mac Book Core Duo with 2 GB RAM. I've never changed any memory setting anywhere, IIRC.
     
  11. xochi

    xochi

    Messages:
    88

Share This Page