[RFC,v2,4/5] spinlock: use wfe to reduce contention on aarch64

  In acquiring a spinlock, cores repeatedly poll the lock variable.
This is replaced by rte_wait_until_equal API.

5~10% performance gain was measured by running spinlock_autotest on
14 isolated cores of ThunderX2.

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>
---
 .../common/include/arch/arm/rte_spinlock.h         | 25 ++++++++++++++++++++++
 .../common/include/generic/rte_spinlock.h          |  2 +-
 2 files changed, 26 insertions(+), 1 deletion(-)
  

>-----Original Message-----
>From: dev <dev-bounces@dpdk.org> On Behalf Of Gavin Hu
>Sent: Wednesday, July 3, 2019 2:29 PM
>To: dev@dpdk.org
>Cc: nd@arm.com
>Subject: [dpdk-dev] [RFC v2 4/5] spinlock: use wfe to reduce contention
>on aarch64
>
>In acquiring a spinlock, cores repeatedly poll the lock variable.
>This is replaced by rte_wait_until_equal API.
>
>5~10% performance gain was measured by running spinlock_autotest
>on
>14 isolated cores of ThunderX2.

Tested on octeontx2 board.

>
>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         | 25
>++++++++++++++++++++++
> .../common/include/generic/rte_spinlock.h          |  2 +-
> 2 files changed, 26 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..f25d17f 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 +16,31 @@ 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.
>+ */
>+#if defined(RTE_USE_WFE) && defined(RTE_ARCH_ARM64)
>+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(
>+		"sevl\n"
>+		"1:	wfe\n"
>+		"2:	ldaxr %w[tmp], %w[locked]\n"
>+		"cbnz   %w[tmp], 1b\n"
>+		"stxr   %w[tmp], %w[one], %w[locked]\n"
>+		"cbnz   %w[tmp], 2b\n"
>+		: [tmp] "=&r" (tmp), [locked] "+Q"(sl->locked)
>+		: [one] "r" (1)
>+		: "cc", "memory");
>+}
>+#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..cf4f15b 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_USE_WFE)
> static inline void
> rte_spinlock_lock(rte_spinlock_t *sl)
> {
>--
>2.7.4