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From: Omkar Maslekar <omkar.maslekar@intel.com>
To: dev@dpdk.org
Cc: bruce.richardson@intel.com, ciara.loftus@intel.com,
	omkar.maslekar@intel.com
Subject: [dpdk-dev] [PATCH v2] EAL: An addition of cache line demote (CLDEMOTE) in rte_prefetch.h
Date: Fri, 11 Sep 2020 09:51:22 -0700
Message-ID: <1599843082-8284-2-git-send-email-omkar.maslekar@intel.com> (raw)
In-Reply-To: <1599843082-8284-1-git-send-email-omkar.maslekar@intel.com>

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 --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
-- 
1.8.3.1


  reply	other threads:[~2020-09-11 16:52 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-10  1:16 [dpdk-dev] [PATCH] " Omkar Maslekar
2020-09-10  1:16 ` Omkar Maslekar
2020-09-10  8:55   ` Bruce Richardson
2020-09-10 23:30     ` Maslekar, Omkar
2020-09-10 22:04   ` David Christensen
2020-09-11 16:51 ` [dpdk-dev] [PATCH v2] " Omkar Maslekar
2020-09-11 16:51   ` Omkar Maslekar [this message]
2020-09-11 21:22 ` [dpdk-dev] [PATCH v3] " Omkar Maslekar
2020-09-11 21:22   ` Omkar Maslekar
2020-09-22  1:59 ` [dpdk-dev] [PATCH v4] eal: add cache-line demote support Omkar Maslekar
2020-09-22  1:59   ` Omkar Maslekar
2020-09-22  8:28     ` Bruce Richardson
2020-09-22 21:53       ` Maslekar, Omkar
2020-10-01  0:28 ` [dpdk-dev] [PATCH v5] " Omkar Maslekar
2020-10-01  0:28   ` Omkar Maslekar
2020-10-08  7:09     ` David Marchand
2020-10-08  9:02       ` Bruce Richardson
2020-10-12  9:41         ` David Marchand
2020-10-08 13:12     ` Jerin Jacob
2020-10-12 10:19 ` [dpdk-dev] [PATCH v6] " Omkar Maslekar
2020-10-12 10:19   ` Omkar Maslekar
2020-10-12 19:31     ` David Christensen
2020-10-13  2:59     ` Ruifeng Wang
2020-10-13 16:20       ` Bruce Richardson
2020-10-14  1:55         ` Ruifeng Wang
2020-10-14  7:14         ` David Marchand
2020-10-14  7:51           ` Ruifeng Wang
2020-10-13  9:43 ` [dpdk-dev] [PATCH v7] " Omkar Maslekar
2020-10-13  9:43   ` Omkar Maslekar
2020-10-14  7:24     ` Ruifeng Wang
2020-10-15  8:01     ` David Marchand
2020-10-15 14:41       ` Maslekar, Omkar
2020-10-15 20:32         ` David Marchand
2020-10-15 15:18 ` [dpdk-dev] [PATCH v8] " Omkar Maslekar
2020-10-15 15:18   ` Omkar Maslekar
2020-10-15 23:20 ` [dpdk-dev] [PATCH v9] " Omkar Maslekar
2020-10-15 23:20   ` Omkar Maslekar
2020-10-16 12:14     ` David Marchand

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