Re: More breakage in native_rdtsc out of line in git-x86 II

[Andi Kleen <andi@firstfloor.org>]

> I think the problem is that the vsyscall/vdso code calls it through
> vread and for that it has to be exported. There seems to be also
> another bug with the old style vsyscalls not using the TSC vread
> that masks it on older glibc
> 
> Stepping with gdb through old style vgettimeofday() confirms that RDTSC is 
> not used.
> 
> A long time ago we had a similar problem once and it was because of a 
> problem exporting the vsyscall variables in vmlinux.lds.S -- looks like that 
> has reappeared.
> 
> I think the new glibc shows it because it uses the vDSO not 
> the older vsyscall and the new vDSO probably still works. Anyways haven't 
> investigated why that is in detail yet, but that's a separate 
> regression.

Actually that seems to be because the test system using the older 
glibc didn't use the TSC because it was marked unstable due a 
unsynchronized TSC. It should not have been -- this is a Core2 
dual core single socket. Will investigate later what happened
there.

-Andi