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SubjectRe: [PATCH 1/5] Skip timer works.patch
Andi Kleen wrote:
>> That is the one that can panic, for now. Fixing the paravirtualized
>> case is easy, but we can't assume paravirtualization just yet.
>>
>
> Hmm, this means standard vmware boot is not reliable unless that magic option
> is set? That doesn't sound good.
>

It doesn't happen often, but it is a possibility that the kernel
calibrates the delay wrong because of timing glitches caused by CPU
migration, paging, or other phenomena which are supposed to be
transparent to the kernel (but cause temporal lapse). In that case, the
kernel may not make enough progress in a spin delay loop to properly
reach the number of microseconds required for N number of timer ticks to
occur. In theory this can happen on a real machine, as SMM mode could
be active, doing USB device emulation or something that takes a while
during the lpj calibration and throwing the computation off.

By changing the parameters (N ticks at K Hz in T seconds), it is easy to
create an unstable measurement that can achieve high failure rates,
although in practice the Linux parameters appear to be reasonable enough
that it is not a major problem.

Zach
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