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SubjectRe: [patch] recover lost ticks
Hi,

On Mon, 15 Mar 1999, Ingo Molnar wrote:

>
> On Mon, 15 Mar 1999, Andrea Arcangeli wrote:
>
> > If the tsc goes as hell gettimeofday will die too, and the TSC is
> > explicity declared from Intel as a really safely trustable thing, so if
> > the TSC will die I expect many other part of the CPU to die too.
>
> (i only pointed out that TSC bugs/inconsistencies (which happened in the
> past) now might have yet another side-effect. [there was a robustness
> claim])

Let me jump in here, real quickly, and just on the matter of broken
TSC's...

There are two (known) cases of these:

1) On Cyrix/IBM/Centaur the TSC will stop if Suspend-on-Halt is
enabled and a HLT is executed. This is usually a very good
thing since power comsuption goes down dramatically, but
the time code has to compensate (and does since somewhere in
2.1.12x).

2) A machine that does a suspend-to-disk or similar, where the CPU
is actually shutdown. TSC will reset. This can happen on any
x86 that does APM.

This is why, IMHO, is not a good idea for other parts of the kernel to use
the TSC directly as a time measure, but instead go through gettimeofday().
The time code should take care of the above.

Cheers,

-Rafael




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