[dpdk-dev] [PATCH v6] eal: add cache-line demote support

[David Christensen]

On 10/12/20 3:19 AM, 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 at intel.com>
> Acked-by: Bruce Richardson <bruce.richardson at intel.com>
> 
> ---
> v6: marked rte_cldemote as experimental
>      added rte_cldemote call in existing app/test_prefetch.c
> 
> v5: documentation updated
>      fixed formatting issue in release notes
>      added Acked-by: Bruce Richardson <bruce.richardson at intel.com>
> *
> v4: updated bold text for title and fixed margin in release notes
> *
> v3: fixed warning regarding whitespace
> *
> v2: documentation updated
> ---
> ---
>   app/test/test_prefetch.c                      |  4 ++++
>   doc/guides/rel_notes/release_20_11.rst        |  7 +++++++
>   lib/librte_eal/arm/include/rte_prefetch_32.h  |  8 ++++++++
>   lib/librte_eal/arm/include/rte_prefetch_64.h  |  8 ++++++++
>   lib/librte_eal/include/generic/rte_prefetch.h | 16 ++++++++++++++++
>   lib/librte_eal/ppc/include/rte_prefetch.h     |  8 ++++++++
>   lib/librte_eal/x86/include/rte_prefetch.h     | 12 ++++++++++++
>   7 files changed, 63 insertions(+)

...snip...

> diff --git a/lib/librte_eal/ppc/include/rte_prefetch.h b/lib/librte_eal/ppc/include/rte_prefetch.h
> index 9ba07c8..9630227 100644
> --- a/lib/librte_eal/ppc/include/rte_prefetch.h
> +++ b/lib/librte_eal/ppc/include/rte_prefetch.h
> @@ -11,6 +11,7 @@
>   #endif
> 
>   #include <rte_common.h>
> +#include <rte_compat.h>
>   #include "generic/rte_prefetch.h"
> 
>   static inline void rte_prefetch0(const volatile void *p)
> @@ -34,6 +35,13 @@ static inline void rte_prefetch_non_temporal(const volatile void *p)
>   	rte_prefetch0(p);
>   }
> 
> +static inline void
> +__rte_experimental
> +rte_cldemote(const volatile void *p)
> +{
> +	RTE_SET_USED(p);
> +}
> +
>   #ifdef __cplusplus
>   }
>   #endif

Don't see an equivalent operation in the 3.1 ISA for POWER processors, 
so NOP is the right implementation.

Acked-by: David Christensen <drc at linux.vnet.ibm.com>