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

[Ruifeng Wang]

> -----Original Message-----
> From: Omkar Maslekar <omkar.maslekar at intel.com>
> Sent: Monday, October 12, 2020 6:20 PM
> To: dev at dpdk.org
> Cc: bruce.richardson at intel.com; ciara.loftus at intel.com;
> omkar.maslekar at intel.com; drc at linux.vnet.ibm.com; jerinj at marvell.com;
> Ruifeng Wang <Ruifeng.Wang at arm.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli at arm.com>
> Subject: [PATCH v6] eal: add cache-line demote support
> 
> 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(+)
> 
> diff --git a/app/test/test_prefetch.c b/app/test/test_prefetch.c index
> 41f219a..5c58d0c 100644
> --- a/app/test/test_prefetch.c
> +++ b/app/test/test_prefetch.c
> @@ -26,7 +26,11 @@
>  	rte_prefetch1(&a);
>  	rte_prefetch2(&a);
> 
> +/* test for marking a line as shared to test cldemote functionality */
> +	rte_cldemote(&a);
> +
>  	return 0;
>  }
> 
> +
>  REGISTER_TEST_COMMAND(prefetch_autotest, test_prefetch); diff --git
> a/doc/guides/rel_notes/release_20_11.rst
> b/doc/guides/rel_notes/release_20_11.rst
> index df227a1..dc402ab 100644
> --- a/doc/guides/rel_notes/release_20_11.rst
> +++ b/doc/guides/rel_notes/release_20_11.rst
> @@ -55,6 +55,13 @@ New Features
>       Also, make sure to start the actual text at the margin.
>       =======================================================
> 
> +* **Added new function rte_cldemote in rte_prefetch.h.**
> +
> +  Added a hardware hint CLDEMOTE, which is similar to prefetch in reverse.
> +  CLDEMOTE moves the cache line to the more remote cache, where it
> + expects  sharing to be efficient. Moving the cache line to a level
> + more distant from  the processor helps to accelerate core-to-core
> communication.
> +

Patch cannot apply. Maybe rebase is needed.

> 
>  Removed Items
>  -------------
> diff --git a/lib/librte_eal/arm/include/rte_prefetch_32.h
> b/lib/librte_eal/arm/include/rte_prefetch_32.h
> index e53420a..062ed27 100644
> --- a/lib/librte_eal/arm/include/rte_prefetch_32.h
> +++ b/lib/librte_eal/arm/include/rte_prefetch_32.h
> @@ -10,6 +10,7 @@
>  #endif
> 
>  #include <rte_common.h>
> +#include <rte_compat.h>
>  #include "generic/rte_prefetch.h"
> 
>  static inline void rte_prefetch0(const volatile void *p) @@ -33,6 +34,13 @@
> static inline void rte_prefetch_non_temporal(const volatile void *p)
>  	rte_prefetch0(p);
>  }
> 
> +static inline void
> +__rte_experimental

See below.

> +rte_cldemote(const volatile void *p)
> +{
> +	RTE_SET_USED(p);
> +}
> +
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/lib/librte_eal/arm/include/rte_prefetch_64.h
> b/lib/librte_eal/arm/include/rte_prefetch_64.h
> index fc2b391..6e5ee07 100644
> --- a/lib/librte_eal/arm/include/rte_prefetch_64.h
> +++ b/lib/librte_eal/arm/include/rte_prefetch_64.h
> @@ -10,6 +10,7 @@
>  #endif
> 
>  #include <rte_common.h>
> +#include <rte_compat.h>
>  #include "generic/rte_prefetch.h"
> 
>  static inline void rte_prefetch0(const volatile void *p) @@ -32,6 +33,13 @@
> static inline void rte_prefetch_non_temporal(const volatile void *p)
>  	asm volatile ("PRFM PLDL1STRM, [%0]" : : "r" (p));  }
> 
> +static inline void
> +__rte_experimental
> +rte_cldemote(const volatile void *p)
> +{
> +	RTE_SET_USED(p);
> +}
> +
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/lib/librte_eal/include/generic/rte_prefetch.h
> b/lib/librte_eal/include/generic/rte_prefetch.h
> index 6e47bdf..3474548 100644
> --- a/lib/librte_eal/include/generic/rte_prefetch.h
> +++ b/lib/librte_eal/include/generic/rte_prefetch.h
> @@ -51,4 +51,20 @@
>   */
>  static inline void rte_prefetch_non_temporal(const volatile void *p);
> 
> +/**
> + * Demote a cache line to a more distant level of cache from the processor.
> + *
> + * CLDEMOTE hints to hardware to move (demote) a cache line from the
> +closest to
> + * the processor to a level more distant from the processor. It is a
> +hint and
> + * not guarantee. rte_cldemote is intended to move the cache line to
> +the more
> + * remote cache, where it expects sharing to be efficient and to
> +indicate that a
> + * line may be accessed by a different core in the future.
> + *
> + * @param p
> + *   Address to demote
> + */
> +static inline void
> +__rte_experimental

1. Experimental tag is only needed in this file. Tags at other places can be removed.
2. To align with other codes, experimental tag can be put above 'static inline void' line.

> +rte_cldemote(const volatile void *p);
> +
>  #endif /* _RTE_PREFETCH_H_ */
> 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
> diff --git a/lib/librte_eal/x86/include/rte_prefetch.h
> b/lib/librte_eal/x86/include/rte_prefetch.h
> index 384c6b3..e1e120e 100644
> --- a/lib/librte_eal/x86/include/rte_prefetch.h
> +++ b/lib/librte_eal/x86/include/rte_prefetch.h
> @@ -10,6 +10,7 @@
>  #endif
> 
>  #include <rte_common.h>
> +#include <rte_compat.h>
>  #include "generic/rte_prefetch.h"
> 
>  static inline void rte_prefetch0(const volatile void *p) @@ -32,6 +33,17 @@
> static inline void rte_prefetch_non_temporal(const volatile void *p)
>  	asm volatile ("prefetchnta %[p]" : : [p] "m" (*(const volatile char
> *)p));  }
> 
> +/*
> + * we're using raw byte codes for now as only the newest compiler
> + * versions support this instruction natively.
> + */
> +static inline void
> +__rte_experimental
> +rte_cldemote(const volatile void *p)
> +{
> +	asm volatile(".byte 0x0f, 0x1c, 0x06" :: "S" (p)); }
> +
>  #ifdef __cplusplus
>  }
>  #endif
> --
> 1.8.3.1