Messages in this thread |  | | Subject | Re: [PATCH] Close small window for vsyscall time inconsistencies | From | Andi Kleen <> | Date | Mon, 07 Apr 2008 13:29:44 +0200 |
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Thomas Gleixner <tglx@linutronix.de> writes: > >> So instead of shooting in the dark, I'd suggest to collect some >> numbers first, > > That's what we did and John's analysis of the problem is pretty > correct.
The source of the problem is that RDTSC is not always 100% sync right?
We debugged a similar problem a long time ago and in that case it was the CPU speculating around the RDTSC. That was stopped by adding the CPUIDs to sync the core.
I would double check that the CPUIDs are still executed as needed on the systems showing the issue.
(the code to turn that on and off is somewhat subtle and breaks occasionally)
Also it was assumed at some point it wasn't needed on P4, but that turned out to be wrong later. Perhaps the enable logic is still not quite right.
Or perhaps the CPUIDs need to be moved inside or outside the seqlocks?
-Andi
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