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Re: [Xen-devel] [PATCH v2 6/6] x86: implement Hyper-V clock source
- To: Jan Beulich <jbeulich@xxxxxxxx>, Wei Liu <wl@xxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 20 Dec 2019 16:07:07 +0000
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- Cc: Xen Development List <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Paul Durrant <pdurrant@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <liuwe@xxxxxxxxxxxxx>, Michael Kelley <mikelley@xxxxxxxxxxxxx>
- Delivery-date: Fri, 20 Dec 2019 16:07:20 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 20/12/2019 16:05, Jan Beulich wrote:
>> + wrmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr);
>> +
>> + /* Get TSC frequency from Hyper-V */
>> + rdmsrl(HV_X64_MSR_TSC_FREQUENCY, freq);
>> + pts->frequency = freq;
>> +
>> + return freq;
>> +}
>> +
>> +static inline uint64_t read_hyperv_timer(void)
>> +{
>> + uint64_t scale, offset, ret, tsc;
>> + uint32_t seq;
>> + const struct ms_hyperv_tsc_page *tsc_page = hyperv_tsc;
>> +
>> + do {
>> + seq = tsc_page->tsc_sequence;
>> +
>> + /* Seq 0 is special. It means the TSC enlightenment is not
>> + * available at the moment. The reference time can only be
>> + * obtained from the Reference Counter MSR.
>> + */
>> + if ( seq == 0 )
>> + {
>> + rdmsrl(HV_X64_MSR_TIME_REF_COUNT, ret);
>> + return ret;
>> + }
>> +
>> + /* rdtsc_ordered already contains a load fence */
>> + tsc = rdtsc_ordered();
>> + scale = tsc_page->tsc_scale;
>> + offset = tsc_page->tsc_offset;
>> +
>> + smp_rmb();
>> +
>> + } while (tsc_page->tsc_sequence != seq);
Style.
~Andrew
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