* George Anzinger <[email protected]> wrote:
> The TSC is such a fast and, usually, accurate answer, I think it
> deserves a little effort to save it. With your new clock code I think
> we could use per cpu TSC counters, read the full 64 bits and, in real
> corner cases, even per cpu conversion "constants" and solve this
> problem.
the problem is, this is the same issue as 'boot-time TSC syncing', but
in disguise: to get any 'per CPU TSC offset' you need to do exactly the
same type of careful all-CPUs-dance to ensure that the TSCs were sampled
at around the same moment in time!
The box where i have these small TSC inconsistencies shows that it's the
bootup synchronization of TSCs that failed to be 100% accurate. Even a 2
usecs error in synchronization can show up as a time-warp - regardless
of whether we keep per-CPU TSC offsets or whether we clear these offsets
back to 0. So it is not a solution to do another type of synchronization
dance. The only solution is to fix the boot-time synchronization (where
the hardware keeps TSCs synchronized all the time), or to switch TSCs
off where this is not possible.
Ingo
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