Re: [dpdk-dev] [PATCH] EAL: An addition of cache line demote (CLDEMOTE) in rte_prefetch.h

[David Christensen <drc@linux.vnet.ibm.com>]

On 9/9/20 6:16 PM, Omkar Maslekar wrote:
> rte_cldemote is similar to a prefetch hint - in reverse. cldemote(addr)
> enables software to hint to hardware that line is likely to be shared.
> Useful in core-to-core communications where cache-line is likely to be
> shared. ARM and PPC implementation is provided with NOP and can be added
> if any equivalent instructions could be used for implementation on those
> architectures.
> 
> Signed-off-by: Omkar Maslekar <omkar.maslekar@intel.com>
> ---

...

> diff --git a/lib/librte_eal/ppc/include/rte_prefetch.h b/lib/librte_eal/ppc/include/rte_prefetch.h
> index 9ba07c8..3fe9655 100644
> --- a/lib/librte_eal/ppc/include/rte_prefetch.h
> +++ b/lib/librte_eal/ppc/include/rte_prefetch.h
> @@ -34,6 +34,11 @@ static inline void rte_prefetch_non_temporal(const volatile void *p)
>   	rte_prefetch0(p);
>   }
> 
> +static inline void rte_cldemote(const volatile void *p)
> +{
> +	RTE_SET_USED(p);
> +}
> +
>   #ifdef __cplusplus
>   }
>   #endif

For POWER there's an instruction defined in the ISA which is the most 
similar, miso (i.e. Make It So), but the instruction is interpreted as a 
NOP in the POWER8/POWER9 CPUs, so NOP is the right choice for PPC at 
this time.

Dave