From: "Morten Brørup" <mb@smartsharesystems.com>
To: thomas@monjalon.net, david.marchand@redhat.com,
honnappa.nagarahalli@arm.com, konstantin.v.ananyev@yandex.ru,
bruce.richardson@intel.com, mattias.ronnblom@ericsson.com
Cc: olivier.matz@6wind.com, andrew.rybchenko@oktetlabs.ru,
dev@dpdk.org, "Morten Brørup" <mb@smartsharesystems.com>
Subject: [PATCH] clarify purpose of empty cache lines
Date: Mon, 4 Sep 2023 10:43:49 +0200 [thread overview]
Message-ID: <20230904084349.12044-1-mb@smartsharesystems.com> (raw)
This patch introduces the generic RTE_CACHE_GUARD macro into the EAL, and
replaces vaguely described empty cache lines in the rte_ring structure
with this macro.
Although the implementation of the rte_ring structure assumes that the
hardware speculatively prefetches 1 cache line, this number can be changed
at build time by modifying RTE_CACHE_GUARD_LINES in rte_config.h.
The background and the RFC was discussed in this thread:
http://inbox.dpdk.org/dev/98CBD80474FA8B44BF855DF32C47DC35D87B39@smartserver.smartshare.dk/
Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
---
config/rte_config.h | 1 +
lib/eal/include/rte_common.h | 13 +++++++++++++
lib/ring/rte_ring_core.h | 6 +++---
3 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/config/rte_config.h b/config/rte_config.h
index 400e44e3cf..cfdf787724 100644
--- a/config/rte_config.h
+++ b/config/rte_config.h
@@ -37,6 +37,7 @@
#define RTE_MAX_TAILQ 32
#define RTE_LOG_DP_LEVEL RTE_LOG_INFO
#define RTE_MAX_VFIO_CONTAINERS 64
+#define RTE_CACHE_GUARD_LINES 1
/* bsd module defines */
#define RTE_CONTIGMEM_MAX_NUM_BUFS 64
diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
index 771c70f2c8..daf1866a32 100644
--- a/lib/eal/include/rte_common.h
+++ b/lib/eal/include/rte_common.h
@@ -527,6 +527,19 @@ rte_is_aligned(const void * const __rte_restrict ptr, const unsigned int align)
/** 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)
+/**
+ * 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__)
+
/*********** PA/IOVA type definitions ********/
/** Physical address */
diff --git a/lib/ring/rte_ring_core.h b/lib/ring/rte_ring_core.h
index d1e59bf9ad..327fdcf28f 100644
--- a/lib/ring/rte_ring_core.h
+++ b/lib/ring/rte_ring_core.h
@@ -126,7 +126,7 @@ struct rte_ring {
uint32_t mask; /**< Mask (size-1) of ring. */
uint32_t capacity; /**< Usable size of ring */
- char pad0 __rte_cache_aligned; /**< empty cache line */
+ RTE_CACHE_GUARD;
/** Ring producer status. */
union {
@@ -135,7 +135,7 @@ struct rte_ring {
struct rte_ring_rts_headtail rts_prod;
} __rte_cache_aligned;
- char pad1 __rte_cache_aligned; /**< empty cache line */
+ RTE_CACHE_GUARD;
/** Ring consumer status. */
union {
@@ -144,7 +144,7 @@ struct rte_ring {
struct rte_ring_rts_headtail rts_cons;
} __rte_cache_aligned;
- char pad2 __rte_cache_aligned; /**< empty cache line */
+ RTE_CACHE_GUARD;
};
#define RING_F_SP_ENQ 0x0001 /**< The default enqueue is "single-producer". */
--
2.17.1
next reply other threads:[~2023-09-04 8:43 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-04 8:43 Morten Brørup [this message]
2023-09-04 9:12 ` Bruce Richardson
2023-10-11 15:59 ` Thomas Monjalon
2023-09-05 6:41 ` Morten Brørup
2023-10-11 23:43 ` Thomas Monjalon
2023-10-12 6:00 ` Morten Brørup
2023-10-12 6:07 ` Morten Brørup
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