[dpdk-dev] [PATCH v3 4/4] kni: introduce c11 atomic into kni fifo synchronization

[Phil Yang <phil.yang@arm.com>]

Syncing the values by adding c11 atomic memory barriers to make sure
the values being synced before updating fifo_write and fifo_read.

Signed-off-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Reviewed-by: Gavin Hu <Gavin.Hu@arm.com>
Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>
---
 .../linuxapp/eal/include/exec-env/rte_kni_common.h |  5 +++
 lib/librte_kni/rte_kni_fifo.h                      | 47 +++++++++++++++++-----
 2 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
index 58e8533..5afa087 100644
--- a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
+++ b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
@@ -55,8 +55,13 @@ struct rte_kni_request {
  * Writing should never overwrite the read position
  */
 struct rte_kni_fifo {
+#ifdef RTE_USE_C11_MEM_MODEL
+	unsigned write;              /**< Next position to be written*/
+	unsigned read;               /**< Next position to be read */
+#else
 	volatile unsigned write;     /**< Next position to be written*/
 	volatile unsigned read;      /**< Next position to be read */
+#endif
 	unsigned len;                /**< Circular buffer length */
 	unsigned elem_size;          /**< Pointer size - for 32/64 bit OS */
 	void *volatile buffer[];     /**< The buffer contains mbuf pointers */
diff --git a/lib/librte_kni/rte_kni_fifo.h b/lib/librte_kni/rte_kni_fifo.h
index 70ac14e..83d31b6 100644
--- a/lib/librte_kni/rte_kni_fifo.h
+++ b/lib/librte_kni/rte_kni_fifo.h
@@ -5,6 +5,36 @@
 
 
 /**
+ * @internal when c11 memory model enabled use c11 atomic memory barrier.
+ * when under non c11 memory model use rte_smp_* memory barrier.
+ *
+ * @param src
+ *   Pointer to the source data.
+ * @param dst
+ *   Pointer to the destination data.
+ * @param value
+ *   Data value.
+ */
+#ifdef RTE_USE_C11_MEM_MODEL
+#define __KNI_LOAD_ACQUIRE(src) ({                         \
+		__atomic_load_n((src), __ATOMIC_ACQUIRE);           \
+	})
+#define __KNI_STORE_RELEASE(dst, value) do {               \
+		__atomic_store_n((dst), value, __ATOMIC_RELEASE);   \
+	} while(0)
+#else
+#define __KNI_LOAD_ACQUIRE(src) ({                         \
+		typeof (*(src)) val = *(src);                       \
+		rte_smp_rmb();                                      \
+		val;                                                \
+	})
+#define __KNI_STORE_RELEASE(dst, value) do {               \
+		*(dst) = value;                                     \
+		rte_smp_wmb();                                      \
+	} while(0)
+#endif
+
+/**
  * Initializes the kni fifo structure
  */
 static void
@@ -29,8 +59,7 @@ kni_fifo_put(struct rte_kni_fifo *fifo, void **data, unsigned num)
 	unsigned i = 0;
 	unsigned fifo_write = fifo->write;
 	unsigned new_write = fifo_write;
-	rte_smp_rmb();
-	unsigned fifo_read = fifo->read;
+	unsigned fifo_read = __KNI_LOAD_ACQUIRE(&fifo->read);
 
 	for (i = 0; i < num; i++) {
 		new_write = (new_write + 1) & (fifo->len - 1);
@@ -40,8 +69,7 @@ kni_fifo_put(struct rte_kni_fifo *fifo, void **data, unsigned num)
 		fifo->buffer[fifo_write] = data[i];
 		fifo_write = new_write;
 	}
-	rte_smp_wmb();
-	fifo->write = fifo_write;
+	__KNI_STORE_RELEASE(&fifo->write, fifo_write);
 	return i;
 }
 
@@ -53,8 +81,7 @@ kni_fifo_get(struct rte_kni_fifo *fifo, void **data, unsigned num)
 {
 	unsigned i = 0;
 	unsigned new_read = fifo->read;
-	rte_smp_rmb();
-	unsigned fifo_write = fifo->write;
+	unsigned fifo_write = __KNI_LOAD_ACQUIRE(&fifo->write);
 
 	for (i = 0; i < num; i++) {
 		if (new_read == fifo_write)
@@ -63,8 +90,7 @@ kni_fifo_get(struct rte_kni_fifo *fifo, void **data, unsigned num)
 		data[i] = fifo->buffer[new_read];
 		new_read = (new_read + 1) & (fifo->len - 1);
 	}
-	rte_smp_rmb();
-	fifo->read = new_read;
+	__KNI_STORE_RELEASE(&fifo->read, new_read);
 	return i;
 }
 
@@ -74,8 +100,7 @@ kni_fifo_get(struct rte_kni_fifo *fifo, void **data, unsigned num)
 static inline uint32_t
 kni_fifo_count(struct rte_kni_fifo *fifo)
 {
-	unsigned fifo_write = fifo->write;
-	rte_smp_rmb();
-	unsigned fifo_read = fifo->read;
+	unsigned fifo_write = __KNI_LOAD_ACQUIRE(&fifo->write);
+	unsigned fifo_read = __KNI_LOAD_ACQUIRE(&fifo->read);
 	return (fifo->len + fifo_write - fifo_read) & (fifo->len - 1);
 }
-- 
2.7.4