>>> On 27.08.13 at 01:42, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> wrote:
> Hyper-V supports a mechanism for retrieving the local API frequency.
"APIC"?
> @@ -27,6 +27,13 @@
> #define HV_X64_MSR_VP_RUNTIME_AVAILABLE (1 << 0)
> /* Partition Reference Counter (HV_X64_MSR_TIME_REF_COUNT) available*/
> #define HV_X64_MSR_TIME_REF_COUNT_AVAILABLE (1 << 1)
> +
> +/* Local APIC timer frequency MSR (HV_X64_MSR_APIC_FREQUENCY) is available */
> +#define HV_X64_MSR_APIC_FREQUENCY_AVAILABLE (1 << 11)
> +
> +/* TSC frequency MSR (HV_X64_MSR_TSC_FREQUENCY) is available */
> +#define HV_X64_MSR_TSC_FREQUENCY_AVAILABLE (1 << 11)
Are these two really the same bit? If so, why two different names?
> @@ -136,6 +143,12 @@
> /* MSR used to read the per-partition time reference counter */
> #define HV_X64_MSR_TIME_REF_COUNT 0x40000020
>
> +/* MSR used to retrive the TSC frequency */
> +#define HV_X64_MSR_TSC_FREQUENCY 0x40000022
> +
> +/* MSR used to retrive the local APIC timer frequency */
> +#define HV_X64_MSR_APIC_FREQUENCY 0x40000023
"retrieve" (twice)?
> @@ -76,6 +77,22 @@ static void __init ms_hyperv_init_platform(void)
> printk(KERN_INFO "HyperV: features 0x%x, hints 0x%x\n",
> ms_hyperv.features, ms_hyperv.hints);
>
> + if (ms_hyperv.features & HV_X64_MSR_APIC_FREQUENCY_AVAILABLE) {
> + /*
> + * There is no need to calibrate APIC timer frequency;
> + * nor is there a need to calibrate timer.
> + */
> + legacy_pic = &null_legacy_pic;
This clearly disables more than just the calibration, so the comment
may be misleading to future readers.
> +
> + /*
> + * Get the APIC frequency.
> + */
> + rdmsrl(HV_X64_MSR_APIC_FREQUENCY, lapic_timer_frequency);
> + lapic_timer_frequency /= HZ;
Is this safe? I.e. are the high 32 bits of the MSR guaranteed to
be zero, now and forever?
> + printk(KERN_INFO "HyperV: LAPIC Timer Frequency: 0x%x\n",
> + lapic_timer_frequency);
As a minor note, I generally recommend using %#x as being one
byte shorter than the spelled out 0x%x.
Jan
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