Andi Kleen wrote:
>
> I don't think it's a good idea for the TSC. There are various
> setups where it is unreliable and also often simulators don't
> implement it correctly. And it's always a valuable workaround
> to be able to turn it off.
>
I dug some more into the TSC code, and found some other annoying stuff:
/*
* Make an educated guess if the TSC is trustworthy and synchronized
* over all CPUs.
*/
__cpuinit int unsynchronized_tsc(void)
{
if (!cpu_has_tsc || tsc_unstable)
return 1;
/*
* Intel systems are normally all synchronized.
* Exceptions must mark TSC as unstable:
*/
if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
/* assume multi socket systems are not synchronized: */
if (num_possible_cpus() > 1)
tsc_unstable = 1;
}
return tsc_unstable;
}
That's a vendor check foul. That should be a CPU feature flag.
Looks like there is some work to be done here.
-hpa
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