Re: [PATCH] lguest-fix-divide-error-implement-sched_clock

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

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