Re: [Xen-devel] [PATCH v4 3/4] nested vmx: optimize for bulk access of virtual VMCS

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.01.13 at 13:00, Dongxiao Xu <dongxiao.xu@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/vmx/vvmx.c
> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> @@ -30,6 +30,7 @@
>  
>  static void nvmx_purge_vvmcs(struct vcpu *v);
>  
> +#define VMCS_BUF_SIZE 500

The biggest batch I can spot is about 60 elements large, so
why 500?

> @@ -83,6 +90,9 @@ void nvmx_vcpu_destroy(struct vcpu *v)
>          list_del(&item->node);
>          xfree(item);
>      }
> +
> +    if ( nvcpu->vvmcx_buf )
> +        xfree(nvcpu->vvmcx_buf);

No need for the if() - xfree() copes quite well with NULL pointers.

> @@ -830,6 +840,35 @@ static void vvmcs_to_shadow(void *vvmcs, unsigned int 
> field)
>      __vmwrite(field, value);
>  }
>  
> +static void vvmcs_to_shadow_bulk(struct vcpu *v, unsigned int n,
> +                                 const u16 *field)
> +{
> +    struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v);
> +    void *vvmcs = nvcpu->nv_vvmcx;
> +    u64 *value = nvcpu->vvmcx_buf;
> +    unsigned int i;
> +
> +    if ( !cpu_has_vmx_vmcs_shadowing )
> +        goto fallback;
> +
> +    if ( !value || n > VMCS_BUF_SIZE )

And then, if you lower that value, be verbose (at lest in debugging
builds) about the buffer size being exceeded.

> --- a/xen/include/asm-x86/hvm/vcpu.h
> +++ b/xen/include/asm-x86/hvm/vcpu.h
> @@ -100,6 +100,8 @@ struct nestedvcpu {
>       */
>      bool_t nv_ioport80;
>      bool_t nv_ioportED;
> +
> +    u64 *vvmcx_buf; /* A temp buffer for data exchange */

VMX-specific field in non-VMX structure? And wouldn't the buffer
anyway more efficiently be per-pCPU instead of per-vCPU?

Jan


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