Re: [Qemu-devel] [PATCH] target-i386: warns users when CPU threads>1 for AMD CPUs

[Eduardo Habkost]

On Tue, Oct 21, 2014 at 11:00:45AM -0400, Wei Huang wrote:
> No AMD CPUs support hyperthreading. When users select threads>1 in
> -smp option, QEMU fixes it by adjusting CPUID_0000_0001_EBX and
> CPUID_8000_0008_ECX based on inputs (sockets, cores, threads);
> so guest VM can boot correctly. However it is still better to gives
> users a warning when such case happens.
> 
> Signed-off-by: Wei Huang <address@hidden>
> ---
[...]
> @@ -2742,6 +2745,20 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
> **errp)
>      mce_init(cpu);
>      qemu_init_vcpu(cs);
>  
> +    /* AMD CPU doesn't support hyperthreading. Even though QEMU fixes
> +     * this issue by adjusting CPUID_0000_0001_EBX and CPUID_8000_0008_ECX
> +     * based on inputs (sockets,cores,threads), it is still better to gives
> +     * users a warning.
> +     *
> +     * NOTE: the following code has to follow qemu_init_vcpu(). Otherwise
> +     * cs->nr_threads hasn't be populated yet and the checking is incorrect.
> +     */
> +    if (IS_AMD_CPU(env) && (cs->nr_threads > 1) && !ht_warned) {

We set CmpLegacy for all non-Intel CPU vendors (and that's what makes
Linux guests ignore HT). So I believe we should warn if
!IS_INTEL_CPU(env) instead of just when it's AMD.

> +        error_report("AMD CPU doesn't support hyperthreading. Please 
> configure"
> +                     " -smp options properly.");
> +        ht_warned = true;
> +    }
> +
>      x86_cpu_apic_realize(cpu, &local_err);
>      if (local_err != NULL) {
>          goto out;
> -- 
> 1.8.3.1
> 

-- 
Eduardo