[dpdk-dev] [PATCH v3] eal/arm64: fix rdtsc precise version

[Linhaifeng <haifeng.lin@huawei.com>]

In order to get more accurate the cntvct_el0 reading,
SW must invoke isb and arch_counter_enforce_ordering.

Reference of linux kernel:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/include/asm/arch_timer.h?h=v5.5#n220

Signed-off-by: Haifeng Lin <haifeng.lin@huawei.com>
---
 .../common/include/arch/arm/rte_atomic_64.h   |  3 +++
 .../common/include/arch/arm/rte_cycles_64.h   | 20 +++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
index 859ae129d..2587f98a2 100644
--- a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
+++ b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
@@ -21,6 +21,7 @@ extern "C" {
 
 #define dsb(opt) asm volatile("dsb " #opt : : : "memory")
 #define dmb(opt) asm volatile("dmb " #opt : : : "memory")
+#define isb()    (asm volatile("isb" : : : "memory"))
 
 #define rte_mb() dsb(sy)
 
@@ -44,6 +45,8 @@ extern "C" {
 
 #define rte_cio_rmb() dmb(oshld)
 
+#define rte_isb() isb()
+
 /*------------------------ 128 bit atomic operations -------------------------*/
 
 #if defined(__ARM_FEATURE_ATOMICS) || defined(RTE_ARM_FEATURE_ATOMICS)
diff --git a/lib/librte_eal/common/include/arch/arm/rte_cycles_64.h b/lib/librte_eal/common/include/arch/arm/rte_cycles_64.h
index 68e7c7338..bc4e3f8e6 100644
--- a/lib/librte_eal/common/include/arch/arm/rte_cycles_64.h
+++ b/lib/librte_eal/common/include/arch/arm/rte_cycles_64.h
@@ -18,6 +18,7 @@ extern "C" {
  *   The time base for this lcore.
  */
 #ifndef RTE_ARM_EAL_RDTSC_USE_PMU
+
 /**
  * This call is portable to any ARMv8 architecture, however, typically
  * cntvct_el0 runs at <= 100MHz and it may be imprecise for some tasks.
@@ -59,11 +60,26 @@ rte_rdtsc(void)
 }
 #endif
 
+#define arch_counter_enforce_ordering(val) do {						\
+	uint64_t tmp, _val = (val);										\
+																	\
+	asm volatile(													\
+	"	eor  %0, %1, %1\n"											\
+	"	add  %0, sp, %0\n"											\
+	"	ldr  xzr, [%0]"												\
+	: "=r" (tmp) : "r" (_val));										\
+} while (0)
+
+
 static inline uint64_t
 rte_rdtsc_precise(void)
 {
-	rte_mb();
-	return rte_rdtsc();
+	uint64_t tsc;
+
+	rte_isb();
+	tsc = rte_rdtsc();
+	arch_counter_enforce_ordering(tsc);
+	return tsc;
 }
 
 static inline uint64_t
-- 
2.24.1.windows.2