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On Friday 07 March 2008, John J. Foster wrote: |
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> Switching to 250Hz looks like it has solved the problem. No time lost |
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> for a little over an hour now, and ntp is syncing properly, I think. |
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> But my reading of the help on this setting led me to believe that |
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> 1000Hz was right for a desktop system. |
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More like "we think that 1000Hz *should* work better than 250Hz, but we |
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don't really know for sure and YMMV..." |
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> Can any explain what this setting actually does, and why it works |
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> now? |
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From /usr/src/linux/kernel/Kconfig.hz: |
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Allows the configuration of the timer frequency. It is |
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customary |
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to have the timer interrupt run at 1000 Hz but 100 Hz may be |
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more |
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beneficial for servers and NUMA systems that do not need to |
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have |
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a fast response for user interaction and that may experience |
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bus |
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contention and cacheline bounces as a result of timer |
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interrupts. |
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Note that the timer interrupt occurs on each processor in an |
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SMP |
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environment leading to NR_CPUS * HZ number of timer interrupts |
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per second. |
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The timer wakes up x times per second and demands that it get attention. |
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Your VM however, cannot control this on the host and the guest kernel |
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interacts in strange ways with the host kernel. |
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Just for interest, what are the Hz settings on host and guest? |
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-- |
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Alan McKinnon |
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alan dot mckinnon at gmail dot com |
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-- |
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gentoo-user@l.g.o mailing list |
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