[SeaBIOS] [PATCH] tsc: use kvmclock for calibration

[Fred .]

It should be kHz not khz.

-            msr, (u32)khz / 1000);
+            msr, (u32)kHz / 1000);

On Thu, Aug 9, 2012 at 2:53 PM, Avi Kivity <avi at redhat.com> wrote:
> On 08/09/2012 02:57 PM, Gerd Hoffmann wrote:
>> Use kvmclock for tsc calibration when running on kvm.  Without this the
>> tsc frequency calibrated by seabios can be *way* off in case the virtual
>> machine is booted on a loaded host.  I've seen seabios calibrating 27
>> instead of ca. 2800 MHz, resulting in timeouts being to short by factor
>> 100.  Which in turn leads to disk I/O errors due to timeouts, especially
>> as I/O requests tend to take a bit longer than usual on a loaded box ...
>
>> +
>> +struct pvclock_vcpu_time_info {
>> +     u32   version;
>> +     u32   pad0;
>> +     u64   tsc_timestamp;
>> +     u64   system_time;
>> +     u32   tsc_to_system_mul;
>> +     s8    tsc_shift;
>> +     u8    flags;
>> +     u8    pad[2];
>> +} PACKED;
>> +
>> +
>> +u64 kvm_tsc_khz(void)
>> +{
>> +    u32 eax, ebx, ecx, edx, msr;
>> +    struct pvclock_vcpu_time_info time;
>> +    u32 addr = (u32)(&time);
>> +    u64 khz;
>> +
>> +    /* check presence and figure msr number */
>> +    cpuid(KVM_CPUID_FEATURES, &eax, &ebx, &ecx, &edx);
>> +    if (eax & KVM_FEATURE_CLOCKSOURCE2) {
>> +        msr = MSR_KVM_SYSTEM_TIME_NEW;
>> +    } else if (eax & KVM_FEATURE_CLOCKSOURCE) {
>> +        msr = MSR_KVM_SYSTEM_TIME;
>> +    } else {
>> +        return 0;
>> +    }
>> +
>> +    /* ask kvm hypervisor to fill struct */
>> +    memset(&time, 0, sizeof(time));
>> +    wrmsr(msr, addr | 1);
>
> How can this work?  There is a 64-byte alignment requirement.
>
>> +    wrmsr(msr, 0);
>> +    if (time.version < 2 || time.tsc_to_system_mul == 0)
>> +        return 0;
>> +
>> +    /* go figure tsc frequency */
>> +    khz = pvclock_tsc_khz(&time);
>> +    dprintf(1, "Using kvmclock, msr 0x%x, tsc %d MHz\n",
>> +            msr, (u32)khz / 1000);
>> +    return khz;
>
> That's a meaningless number.  You can be migrated to a cpu or a machine
> with very different tsc.
>
> You want accurate time on kvm, don't use the tsc.
>
>
> --
> error compiling committee.c: too many arguments to function
>
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