[PATCH] clarify purpose of empty cache lines

[Thomas Monjalon]

04/09/2023 10:43, Morten Brørup:
>  /** Force minimum cache line alignment. */
>  #define __rte_cache_min_aligned __rte_aligned(RTE_CACHE_LINE_MIN_SIZE)
>  
> +#define _RTE_CACHE_GUARD_HELPER2(unique) \
> +		char cache_guard_ ## unique[RTE_CACHE_LINE_SIZE * RTE_CACHE_GUARD_LINES] \
> +		__rte_cache_aligned
> +#define _RTE_CACHE_GUARD_HELPER1(unique) _RTE_CACHE_GUARD_HELPER2(unique)

What is the reason for this intermediate helper macro?

> +/**
> + * Empty cache lines, to guard against false sharing-like effects
> + * on systems with a next-N-lines hardware prefetcher.
> + *
> + * Use as spacing between data accessed by different lcores,
> + * to prevent cache thrashing on hardware with speculative prefetching.
> + */
> +#define RTE_CACHE_GUARD _RTE_CACHE_GUARD_HELPER1(__COUNTER__)