>However, if you have a reasonable limit on how long you may be
>interrupted (1/2 of the major increment) you can do this without
>loops:
>
> mov (xtime_sec),%ecx
> mov (xtime_usec),%eax
> mov (xtime_sec),%edx
> cmp %eax,500000 ; 1/2 of the major increment
> jb 1f
> mov %ecx,%edx
>1: ; Result in %edx:%eax
>
>If the minor counter is less than halfway to rollover, it is safe to
>assume the value read immediately *after* is stable; if it's more than
>halfway, that the value read immediately *before* is stable. One
>advantage with not having a loop is that you don't bias the output.
Maybe we aren't talking about the same thing, but my point is that if you
don't use any lock and you don't __cli() the other cpu, you could _always_
have %ecx == %edx even if the other CPU has updated only usec (because
it's been interrupted a bit before having the time to increase tv_sec).
Andrea Arcangeli
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