Tickless Linux?

Discussion in 'Linux Guest OS Discussion' started by slamb, Jul 23, 2007.

  1. slamb

    slamb

    Messages:
    11
    Has anyone gotten tickless Linux to work under Parallels?

    I have not - under Parallels Desktop for Mac build 3214, I've compiled a tickless kernel, but according to powertop it still is waking up by timer every HZ seconds, and I don't see the magic message displayed:

    Code:
            printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
                   smp_processor_id());
    It looks like Parallels only supports a few time sources:

    Code:
    $ sudo cat /sys/devices/system/clocksource/*/available_clocksource
    pit jiffies tsc 
    
    not any of the "apic", "hpet", "i8253", and "vmiclock" support CLOCK_EVT_FEAT_ONESHOT, which is needed for tickless operation. Specifically, Local APIC support is disabled in the BIOS, and when I try to enable it by passing in the suggested "lapic" option, it said it was unable to do so.

    Anyone gotten any of these other time sources to work?
     
  2. slamb

    slamb

    Messages:
    11
    Tickless lowers power consumption from 20-25% to 2%

    Interestingly, tickless works in VMware Fusion, so I was able to get a comparison. It makes a huge difference for power consumption. CentOS 5 by default fires a timer off 1000 times a second. That makes the thing use crazy amounts of CPU - my guest was using 20-25% of the host CPU when idle. When using a tickless kernel, it uses only 2% CPU. So my battery lasts much longer.
     
  3. Ynot

    Ynot Kilo Poster

    Messages:
    387
    Unfortunately, there are no APIC support in current version of Parallels. It will be there in future versions.
     

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