On Tue, Jun 23, 2020 at 02:35:30PM +0800, Like Xu wrote:
> The aperf/mperf are used to report current CPU frequency after 7d5905dc14a
> "x86 / CPU: Always show current CPU frequency in /proc/cpuinfo". But guest
> kernel always reports a fixed VCPU frequency in the /proc/cpuinfo, which
> may confuse users especially when turbo is enabled on the host.
>
> Emulate guest APERF/MPERF capability based their values on the host.
>
> Co-developed-by: Li RongQing <[email protected]>
> Signed-off-by: Li RongQing <[email protected]>
> Reviewed-by: Chai Wen <[email protected]>
> Reviewed-by: Jia Lina <[email protected]>
> Signed-off-by: Like Xu <[email protected]>
> ---
...
> @@ -8312,7 +8376,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> dm_request_for_irq_injection(vcpu) &&
> kvm_cpu_accept_dm_intr(vcpu);
> fastpath_t exit_fastpath;
> -
> + u64 enter_mperf = 0, enter_aperf = 0, exit_mperf = 0, exit_aperf = 0;
> bool req_immediate_exit = false;
>
> if (kvm_request_pending(vcpu)) {
> @@ -8516,8 +8580,17 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD;
> }
>
> + if (unlikely(vcpu->arch.hwp.hw_coord_fb_cap))
> + get_host_amperf(&enter_mperf, &enter_aperf);
> +
> exit_fastpath = kvm_x86_ops.run(vcpu);
>
> + if (unlikely(vcpu->arch.hwp.hw_coord_fb_cap)) {
> + get_host_amperf(&exit_mperf, &exit_aperf);
> + vcpu_update_amperf(vcpu, get_amperf_delta(enter_aperf,
> exit_aperf),
> + get_amperf_delta(enter_mperf, exit_mperf));
> + }
> +
Is there an alternative approach that doesn't require 4 RDMSRs on every VMX
round trip? That's literally more expensive than VM-Enter + VM-Exit
combined.
E.g. what about adding KVM_X86_DISABLE_EXITS_APERF_MPERF and exposing the
MSRs for read when that capability is enabled?
