[dpdk-dev] [PATCH v2] examples/vhost: fix statistics error

[Jianfeng Tan <jianfeng.tan@intel.com>]

This issue was discovered under the case of software vm2vm
fowarding. When pkts are received from virtio device 0 and
tx_route to virtio device 1, tx of device 0 is not updated.

To fix this problem, we check each rx/tx branch to update
stats. Besides, the stats are printed at a separated thread,
so we design a mechanism to make sure unreasonable data will
not show.

Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
Tested-by: Qian Xu <qian.q.xu@intel.com>
---
 examples/vhost/main.c | 71 ++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 51 insertions(+), 20 deletions(-)

diff --git a/examples/vhost/main.c b/examples/vhost/main.c
index 9bfda6d..1863dc3 100644
--- a/examples/vhost/main.c
+++ b/examples/vhost/main.c
@@ -312,12 +312,25 @@ struct ipv4_hdr {
 
 /* Per-device statistics struct */
 struct device_statistics {
-	uint64_t tx_total;
+	/* rx: from vhost to virtio; tx: from virtio to vhost */
+
+	/* write-only by datapath threads */
+	/* for non zero-copy case, pkts may be enqueued by any lcore */
 	rte_atomic64_t rx_total_atomic;
-	uint64_t rx_total;
-	uint64_t tx;
 	rte_atomic64_t rx_atomic;
+	/* for zero-copy case */
+	uint64_t rx_total;
 	uint64_t rx;
+	/* write-only by corresponding datapath thread */
+	uint64_t tx_total;
+	uint64_t tx;
+
+	/* write-only by print-stats threads */
+	uint64_t rx_total_p;
+	uint64_t rx_p;
+	uint64_t tx_total_p;
+	uint64_t tx_p;
+
 } __rte_cache_aligned;
 struct device_statistics dev_statistics[MAX_DEVICES];
 
@@ -2787,7 +2800,6 @@ static void
 print_stats(void)
 {
 	struct virtio_net_data_ll *dev_ll;
-	uint64_t tx_dropped, rx_dropped;
 	uint64_t tx, tx_total, rx, rx_total;
 	uint32_t device_fh;
 	const char clr[] = { 27, '[', '2', 'J', '\0' };
@@ -2804,9 +2816,18 @@ print_stats(void)
 		dev_ll = ll_root_used;
 		while (dev_ll != NULL) {
 			device_fh = (uint32_t)dev_ll->vdev->dev->device_fh;
-			tx_total = dev_statistics[device_fh].tx_total;
-			tx = dev_statistics[device_fh].tx;
-			tx_dropped = tx_total - tx;
+
+			tx_total = dev_statistics[device_fh].tx_total -
+				dev_statistics[device_fh].tx_total_p;
+			tx = dev_statistics[device_fh].tx -
+				dev_statistics[device_fh].tx_p;
+			/* Because we do not use a lock to control the access of tx_total
+			 * and tx in dev_statistics, tx may be greater than tx_total. If
+			 * this happens, we'll count those redundant tx next time.
+			 */
+			if (unlikely(tx_total < tx))
+				tx = tx_total;
+
 			if (zero_copy == 0) {
 				rx_total = rte_atomic64_read(
 					&dev_statistics[device_fh].rx_total_atomic);
@@ -2816,22 +2837,32 @@ print_stats(void)
 				rx_total = dev_statistics[device_fh].rx_total;
 				rx = dev_statistics[device_fh].rx;
 			}
-			rx_dropped = rx_total - rx;
+			rx_total -= dev_statistics[device_fh].rx_total_p;
+			rx -= dev_statistics[device_fh].rx_p;
+			if (unlikely(rx_total < rx))
+				rx = rx_total;
+
+			dev_statistics[device_fh].rx_total_p += rx_total;
+			dev_statistics[device_fh].rx_p += rx;
+			dev_statistics[device_fh].tx_total_p += tx_total;
+			dev_statistics[device_fh].tx_p += tx;
 
 			printf("\nStatistics for device %"PRIu32" ------------------------------"
-					"\nTX total: 		%"PRIu64""
-					"\nTX dropped: 		%"PRIu64""
-					"\nTX successful: 		%"PRIu64""
-					"\nRX total: 		%"PRIu64""
-					"\nRX dropped: 		%"PRIu64""
-					"\nRX successful: 		%"PRIu64"",
+					"\n\tTX total:\t\t\t%"PRIu64""
+					"\n\tTX dropped:\t\t\t%"PRIu64""
+					"\n\tTX successful:\t\t\t%"PRIu64""
+					"\n\tRX total:\t\t\t%"PRIu64""
+					"\n\tRX dropped:\t\t\t%"PRIu64""
+					"\n\tRX successful:\t\t\t%"PRIu64"",
 					device_fh,
-					tx_total,
-					tx_dropped,
-					tx,
-					rx_total,
-					rx_dropped,
-					rx);
+					dev_statistics[device_fh].tx_total_p,
+					(dev_statistics[device_fh].tx_total_p
+						- dev_statistics[device_fh].tx_p),
+					dev_statistics[device_fh].tx_p,
+					dev_statistics[device_fh].rx_total_p,
+					(dev_statistics[device_fh].rx_total_p
+						- dev_statistics[device_fh].rx_p),
+					dev_statistics[device_fh].rx_p);
 
 			dev_ll = dev_ll->next;
 		}
-- 
2.1.4