Re: [UNIKRAFT PATCH 2/2] arch/arm: Provide ukarch_spinwait noop for ARM

[Costin Lupu <costin.lupu@xxxxxxxxx>]

Reviewed-by: Costin Lupu <costin.lupu@xxxxxxxxx>

On 7/23/20 11:15 AM, Alexander Jung wrote:
> ARM does not support a pause-type instruction for busy spin wait
> operations.  This commit provides the same alias to be used in
> instances where it is required but defaults to a blank operation.
> 
> Signed-off-by: Alexander Jung <alexander.jung@xxxxxxxxx>
> ---
>  arch/arm/arm/include/uk/asm/lcpu.h   | 5 +++++
>  arch/arm/arm64/include/uk/asm/lcpu.h | 5 +++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/arch/arm/arm/include/uk/asm/lcpu.h 
> b/arch/arm/arm/include/uk/asm/lcpu.h
> index cdeffc3..f38ffb9 100644
> --- a/arch/arm/arm/include/uk/asm/lcpu.h
> +++ b/arch/arm/arm/include/uk/asm/lcpu.h
> @@ -57,3 +57,8 @@ struct __regs {
>  #ifndef wmb
>  #define wmb() __asm__("dsb" : : : "memory")
>  #endif
> +
> +static inline void ukarch_spinwait(void)
> +{
> +     /* Intelligent busy wait not supported on arm. */
> +}
> diff --git a/arch/arm/arm64/include/uk/asm/lcpu.h 
> b/arch/arm/arm64/include/uk/asm/lcpu.h
> index 45d1b23..51e17ad 100644
> --- a/arch/arm/arm64/include/uk/asm/lcpu.h
> +++ b/arch/arm/arm64/include/uk/asm/lcpu.h
> @@ -146,4 +146,9 @@ static inline unsigned long ukarch_read_sp(void)
>       return sp;
>  }
>  
> +static inline void ukarch_spinwait(void)
> +{
> +     /* Intelligent busy wait not supported on arm64. */
> +}
> +
>  #endif /* __ASSEMBLY__ */
>