Re: [Qemu-devel] [PATCH v6 2/3] target-i386: reorganize TSC rate setting code

[Eduardo Habkost]

On Tue, Nov 24, 2015 at 11:33:56AM +0800, Haozhong Zhang wrote:
> Following changes are made to the TSC rate setting code in
> kvm_arch_init_vcpu():
>  * The code is moved to a new function kvm_arch_set_tsc_khz().
>  * If kvm_arch_set_tsc_khz() fails, i.e. following two conditions are
>    both satisfied:
>    * KVM does not support the TSC scaling or it fails to set vcpu's
>      TSC rate by KVM_SET_TSC_KHZ,
>    * the TSC rate to be set is different than the value currently used
>      by KVM,
>    then kvm_arch_init_vcpu() will fail. Prevously,
>    * the lack of TSC scaling never failed kvm_arch_init_vcpu(),
>    * the failure of KVM_SET_TSC_KHZ failed kvm_arch_init_vcpu()
>      unconditionally, even though the TSC rate to be set is identical
>      to the value currently used by KVM.
> 
> Signed-off-by: Haozhong Zhang <address@hidden>

Reviewed-by: Eduardo Habkost <address@hidden>

> ---
>  target-i386/kvm.c | 40 +++++++++++++++++++++++++++++++++-------
>  1 file changed, 33 insertions(+), 7 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index a0fe9d4..1e811ee 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -524,6 +524,36 @@ static bool hyperv_enabled(X86CPU *cpu)
>              cpu->hyperv_runtime);
>  }
>  
> +static int kvm_arch_set_tsc_khz(CPUState *cs)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    int r;
> +
> +    if (!env->tsc_khz) {
> +        return 0;
> +    }
> +
> +    r = kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL) ?
> +        kvm_vcpu_ioctl(cs, KVM_SET_TSC_KHZ, env->tsc_khz) :
> +        -ENOTSUP;
> +    if (r < 0) {
> +        /* When KVM_SET_TSC_KHZ fails, it's an error only if the current
> +         * TSC frequency doesn't match the one we want.
> +         */
> +        int cur_freq = kvm_check_extension(cs->kvm_state, 
> KVM_CAP_GET_TSC_KHZ) ?
> +                       kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) :
> +                       -ENOTSUP;
> +        if (cur_freq <= 0 || cur_freq != env->tsc_khz) {
> +            error_report("warning: TSC frequency mismatch between "
> +                         "VM and host, and TSC scaling unavailable");
> +            return r;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>  static Error *invtsc_mig_blocker;
>  
>  #define KVM_MAX_CPUID_ENTRIES  100
> @@ -823,13 +853,9 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          return r;
>      }
>  
> -    r = kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL);
> -    if (r && env->tsc_khz) {
> -        r = kvm_vcpu_ioctl(cs, KVM_SET_TSC_KHZ, env->tsc_khz);
> -        if (r < 0) {
> -            fprintf(stderr, "KVM_SET_TSC_KHZ failed\n");
> -            return r;
> -        }
> +    r = kvm_arch_set_tsc_khz(cs);
> +    if (r < 0) {
> +        return r;
>      }
>  
>      /* vcpu's TSC frequency is either specified by user, or following
> -- 
> 2.4.8
> 

-- 
Eduardo