linux-kernel - Re: [PATCH v3 1/4] KVM: x86/hyperv: Calculate APIC bus frequency for hyper-v

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Message-ID: <7e614fab-8f91-4a91-bfbf-1b02b9f12cdb@intel.com>
Date: Fri, 29 Dec 2023 12:20:57 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Vishal Annapurve <vannapurve@...gle.com>, Jim Mattson <jmattson@...gle.com>,
 Maxim Levitsky <mlevitsk@...hat.com>
Cc: isaku.yamahata@...il.com
Subject: Re: [PATCH v3 1/4] KVM: x86/hyperv: Calculate APIC bus frequency for
 hyper-v

On 12/21/2023 1:26 PM, Xiaoyao Li wrote:
> On 12/19/2023 4:34 PM, Isaku Yamahata wrote:
>> Remove APIC_BUS_FREUQNCY and calculate it based on APIC bus cycles per 
>> NS.
>> APIC_BUS_FREUQNCY is used only for HV_X64_MSR_APIC_FREQUENCY.  The MSR is
>> not frequently read, calculate it every time.
>>
>> In order to make APIC bus frequency configurable, we need to make make 
>> two
> 
> two 'make', please drop one.

With this and other typos pointed by Maxim fixed.

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

>> related constants into variables.  APIC_BUS_FREUQNCY and 
>> APIC_BUS_CYCLE_NS.
>> One can be calculated from the other.
>>     APIC_BUS_CYCLES_NS = 1000 * 1000 * 1000 / APIC_BUS_FREQUENCY.
>> By removing APIC_BUS_FREQUENCY, we need to track only single variable
>> instead of two.
>>
>> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
>> ---
>> Changes v3:
>> - Newly added according to Maxim Levistsky suggestion.
>> ---
>>   arch/x86/kvm/hyperv.c | 2 +-
>>   arch/x86/kvm/lapic.h  | 1 -
>>   2 files changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
>> index 238afd7335e4..a40ca2fef58c 100644
>> --- a/arch/x86/kvm/hyperv.c
>> +++ b/arch/x86/kvm/hyperv.c
>> @@ -1687,7 +1687,7 @@ static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, 
>> u32 msr, u64 *pdata,
>>           data = (u64)vcpu->arch.virtual_tsc_khz * 1000;
>>           break;
>>       case HV_X64_MSR_APIC_FREQUENCY:
>> -        data = APIC_BUS_FREQUENCY;
>> +        data = div64_u64(1000000000ULL, APIC_BUS_CYCLE_NS);
>>           break;
>>       default:
>>           kvm_pr_unimpl_rdmsr(vcpu, msr);
>> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
>> index 0a0ea4b5dd8c..a20cb006b6c8 100644
>> --- a/arch/x86/kvm/lapic.h
>> +++ b/arch/x86/kvm/lapic.h
>> @@ -17,7 +17,6 @@
>>   #define APIC_DEST_MASK            0x800
>>   #define APIC_BUS_CYCLE_NS       1
>> -#define APIC_BUS_FREQUENCY      (1000000000ULL / APIC_BUS_CYCLE_NS)
>>   #define APIC_BROADCAST            0xFF
>>   #define X2APIC_BROADCAST        0xFFFFFFFFul
> 
>