linux-kernel - Re: [PATCH V4 1/4] KVM: x86: hyper-v: Calculate APIC bus frequency for Hyper-V

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Message-ID: <081f049fd8601ee81d9883797acafa006e7991c4.camel@intel.com>
Date: Tue, 16 Apr 2024 17:07:58 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "jmattson@...gle.com" <jmattson@...gle.com>, "Gao, Chao"
	<chao.gao@...el.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>, "Annapurve, Vishal"
	<vannapurve@...gle.com>, "Chatre, Reinette" <reinette.chatre@...el.com>, "Li,
 Xiaoyao" <xiaoyao.li@...el.com>, "Aktas, Erdem" <erdemaktas@...gle.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "mlevitsk@...hat.com"
	<mlevitsk@...hat.com>, "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4 1/4] KVM: x86: hyper-v: Calculate APIC bus frequency
 for Hyper-V

On Thu, 2024-03-21 at 09:37 -0700, Reinette Chatre wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Remove APIC_BUS_FREQUENCY and calculate it based on nanoseconds per APIC
> bus cycle.  APIC_BUS_FREQUENCY is used only for HV_X64_MSR_APIC_FREQUENCY.
> The MSR is not frequently read, calculate it every time.
> 
> There are two constants related to the APIC bus frequency:
> APIC_BUS_FREQUENCY and APIC_BUS_CYCLE_NS.
> Only one value is required because one can be calculated from the other:
>    APIC_BUS_CYCLES_NS = 1000 * 1000 * 1000 / APIC_BUS_FREQUENCY.
> 
> Remove APIC_BUS_FREQUENCY and instead calculate it when needed.
> This prepares for support of configurable APIC bus frequency by
> requiring to change only a single variable.
> 
> Suggested-by: Maxim Levitsky <maximlevitsky@...il.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Reviewed-by: Maxim Levitsky <maximlevitsky@...il.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> [reinette: rework changelog]
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>