diff mbox series

[v2] EAL: An addition of cache line demote (CLDEMOTE) in rte_prefetch.h

Message ID 1599843082-8284-2-git-send-email-omkar.maslekar@intel.com (mailing list archive)
State Superseded, archived
Delegated to: David Marchand
Headers
Series [v2] EAL: An addition of cache line demote (CLDEMOTE) in rte_prefetch.h |

Checks

Context Check Description
ci/checkpatch warning coding style issues
ci/iol-broadcom-Performance success Performance Testing PASS
ci/iol-broadcom-Functional success Functional Testing PASS
ci/iol-testing success Testing PASS
ci/iol-intel-Functional success Functional Testing PASS
ci/iol-intel-Performance success Performance Testing PASS
ci/travis-robot success Travis build: passed
ci/iol-mellanox-Performance success Performance Testing PASS
ci/Intel-compilation success Compilation OK

Commit Message

Omkar Maslekar Sept. 11, 2020, 4:51 p.m. UTC 
  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>

---
v2: documentation updated
---
---
 doc/guides/rel_notes/release_20_11.rst        |  8 +++++++-
 lib/librte_eal/arm/include/rte_prefetch_32.h  |  5 +++++
 lib/librte_eal/arm/include/rte_prefetch_64.h  |  5 +++++
 lib/librte_eal/include/generic/rte_prefetch.h | 13 +++++++++++++
 lib/librte_eal/ppc/include/rte_prefetch.h     |  5 +++++
 lib/librte_eal/x86/include/rte_prefetch.h     |  9 +++++++++
 6 files changed, 44 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/doc/guides/rel_notes/release_20_11.rst b/doc/guides/rel_notes/release_20_11.rst
index df227a1..b86e9e0 100644
--- a/doc/guides/rel_notes/release_20_11.rst
+++ b/doc/guides/rel_notes/release_20_11.rst
@@ -26,7 +26,7 @@  New Features
 
 .. This section should contain new features added in this release.
    Sample format:
-
+   
    * **Add a title in the past tense with a full stop.**
 
      Add a short 1-2 sentence description in the past tense.
@@ -55,6 +55,12 @@  New Features
      Also, make sure to start the actual text at the margin.
      =======================================================
 
+     EAL: 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.
 
 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..ad91edd 100644
--- a/lib/librte_eal/arm/include/rte_prefetch_32.h
+++ b/lib/librte_eal/arm/include/rte_prefetch_32.h
@@ -33,6 +33,11 @@  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
diff --git a/lib/librte_eal/arm/include/rte_prefetch_64.h b/lib/librte_eal/arm/include/rte_prefetch_64.h
index fc2b391..35d278a 100644
--- a/lib/librte_eal/arm/include/rte_prefetch_64.h
+++ b/lib/librte_eal/arm/include/rte_prefetch_64.h
@@ -32,6 +32,11 @@  static inline void rte_prefetch_non_temporal(const volatile void *p)
 	asm volatile ("PRFM PLDL1STRM, [%0]" : : "r" (p));
 }
 
+static inline void 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..8742412 100644
--- a/lib/librte_eal/include/generic/rte_prefetch.h
+++ b/lib/librte_eal/include/generic/rte_prefetch.h
@@ -51,4 +51,17 @@ 
  */
 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 speed up things at the producer,
+ * in the producer-consumer case.
+ *
+ * @param p
+ *   Address to demote
+ */
+static inline void 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..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
diff --git a/lib/librte_eal/x86/include/rte_prefetch.h b/lib/librte_eal/x86/include/rte_prefetch.h
index 384c6b3..029d06e 100644
--- a/lib/librte_eal/x86/include/rte_prefetch.h
+++ b/lib/librte_eal/x86/include/rte_prefetch.h
@@ -32,6 +32,15 @@  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_cldemote(const volatile void *p)
+{
+	asm volatile(".byte 0x0f, 0x1c, 0x06" :: "S" (p));
+}
+
 #ifdef __cplusplus
 }
 #endif