Messages in this thread | | | Date | Thu, 29 Nov 2007 23:04:40 -0800 | From | "H. Peter Anvin" <> | Subject | Re: constant_tsc and TSC unstable |
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Paul Rolland (ポール・ロラン) wrote: > >> Note that once TSC is disabled (it's using "jiffies" as far >> as I can see), ntpd constantly speeds up and slows down the >> clock, it jumps +/- 0.5sec every several minutes or hours - >> I guess that's when ntpd process gets moved from one core >> to another for whatever reason. And an interesting thing >> is that with 64bits kernel this TSC problem does not occur >> on this very machine. > Hmmmm.... That could make it a problem related to kernel rather than CPU. > >> Something similar is reported on AMD X2 64 machines as well -- >> can't check right now. > If I recall correctly, issues with AMD X2 where related to TSC being > independant for each core and not constant (speed depending of C state). > But the reason I raise the issue is that the Core2 reports constant TSC, > so there is (IMHO) no reason for that. >
Well, "constant" doesn't mean "synchronized", but it might very well be that the Core2 could really benefit from synchronizing the TSCs manually like we used to.
On the other hand, I notice that most of the TSC warp values are relatively close to 2^32, so this could be a specific bug.
-hpa
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