From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Ladi Prosek <lprosek@redhat.com>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com
Subject: Re: [PATCH v2] KVM: hyperv: support HV_X64_MSR_TSC_FREQUENCY and HV_X64_MSR_APIC_FREQUENCY
Date: Wed, 26 Jul 2017 14:49:54 +0200 [thread overview]
Message-ID: <20170726124954.GA2551@flask> (raw)
In-Reply-To: <20170726113259.11395-1-lprosek@redhat.com>
2017-07-26 13:32+0200, Ladi Prosek:
> It has been experimentally confirmed that supporting these two MSRs is one
> of the necessary conditions for nested Hyper-V to use the TSC page. Modern
> Windows guests are noticeably slower when they fall back to reading
> timestamps from the HV_X64_MSR_TIME_REF_COUNT MSR instead of using the TSC
> page.
>
> The newly supported MSRs are advertised with the AccessFrequencyRegs
> partition privilege flag and CPUID.40000003H:EDX[8] "Support for
> determining timer frequencies is available" (both outside of the scope of
> this KVM patch).
> Signed-off-by: Ladi Prosek <lprosek@redhat.com>
> ---
>
> v1->v2:
> * HV_X64_MSR_TSC_FREQUENCY now based on vcpu->arch.virtual_tsc_khz (Radim)
> * Removed both MSRs from the partition-wide list as the implementation is
> no longer vcpu agnostic
I like that we don't have to add a capability to expose this feature to
the userspace,
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
next prev parent reply other threads:[~2017-07-26 12:49 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-26 11:32 [PATCH v2] KVM: hyperv: support HV_X64_MSR_TSC_FREQUENCY and HV_X64_MSR_APIC_FREQUENCY Ladi Prosek
2017-07-26 12:49 ` Radim Krčmář [this message]
2017-07-27 14:23 ` Paolo Bonzini
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