Re: constant_tsc and TSC unstable

["H. Peter Anvin" <hpa@zytor.com>]

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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