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From: Gavin Hu <gavin.hu@arm.com>
To: dev@dpdk.org
Cc: nd@arm.com, david.marchand@redhat.com, konstantin.ananyev@intel.com,
thomas@monjalon.net, stephen@networkplumber.org, hemant.agrawal@nxp.com,
jerinj@marvell.com, pbhagavatula@marvell.com, Honnappa.Nagarahalli@arm.com,
ruifeng.wang@arm.com, phil.yang@arm.com, steve.capper@arm.com
Date: Mon, 21 Oct 2019 17:47:56 +0800
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Subject: [dpdk-dev] [PATCH v8 3/6] spinlock: use wfe to reduce contention on
aarch64
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In acquiring a spinlock, cores repeatedly poll the lock variable.
This is replaced by rte_wait_until_equal API.
Running the micro benchmarking and the testpmd and l3fwd traffic tests
on ThunderX2, Ampere eMAG80 and Arm N1SDP, everything went well and no
notable performance gain nor degradation was measured.
Signed-off-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Tested-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
---
.../common/include/arch/arm/rte_spinlock.h | 26 ++++++++++++++++++++++
.../common/include/generic/rte_spinlock.h | 2 +-
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/lib/librte_eal/common/include/arch/arm/rte_spinlock.h b/lib/librte_eal/common/include/arch/arm/rte_spinlock.h
index 1a6916b..c69bed1 100644
--- a/lib/librte_eal/common/include/arch/arm/rte_spinlock.h
+++ b/lib/librte_eal/common/include/arch/arm/rte_spinlock.h
@@ -16,6 +16,32 @@ extern "C" {
#include <rte_common.h>
#include "generic/rte_spinlock.h"
+/* armv7a does support WFE, but an explicit wake-up signal using SEV is
+ * required (must be preceded by DSB to drain the store buffer) and
+ * this is less performant, so keep armv7a implementation unchanged.
+ */
+#ifdef RTE_ARM_USE_WFE
+static inline void
+rte_spinlock_lock(rte_spinlock_t *sl)
+{
+ unsigned int tmp;
+ /* http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.
+ * faqs/ka16809.html
+ */
+ asm volatile(
+ "1: ldaxr %w[tmp], %w[locked]\n"
+ "cbnz %w[tmp], 2f\n"
+ "stxr %w[tmp], %w[one], %w[locked]\n"
+ "cbnz %w[tmp], 1b\n"
+ "ret\n"
+ "2: sevl\n"
+ "wfe\n"
+ "jmp 1b\n"
+ : [tmp] "=&r" (tmp), [locked] "+Q"(sl->locked)
+ : [one] "r" (1)
+}
+#endif
+
static inline int rte_tm_supported(void)
{
return 0;
diff --git a/lib/librte_eal/common/include/generic/rte_spinlock.h b/lib/librte_eal/common/include/generic/rte_spinlock.h
index 87ae7a4..cf57c72 100644
--- a/lib/librte_eal/common/include/generic/rte_spinlock.h
+++ b/lib/librte_eal/common/include/generic/rte_spinlock.h
@@ -57,7 +57,7 @@ rte_spinlock_init(rte_spinlock_t *sl)
static inline void
rte_spinlock_lock(rte_spinlock_t *sl);
-#ifdef RTE_FORCE_INTRINSICS
+#if defined(RTE_FORCE_INTRINSICS) && !defined(RTE_ARM_USE_WFE)
static inline void
rte_spinlock_lock(rte_spinlock_t *sl)
{
--
2.7.4