[dpdk-dev] [PATCH] net/mlx5: use open/read/close for reading ib stat

[Mohsin Shaikh]

fgets(3)/fread(3)/fscanf(3) etc. use mmap(2)/munmap(2) which leads
to TLB shootdown interrupts to all dpdk app cores including RX cores.
This can cause packet drops. Use read(2)/write(2) instead.

Bugzilla ID: 440
Cc: stable at dpdk.org

Signed-off-by: Mohsin Shaikh <mohsinshaikh at niometrics.com>
---
 drivers/net/mlx5/mlx5_stats.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_stats.c b/drivers/net/mlx5/mlx5_stats.c
index 7603502..b2c09d8 100644
--- a/drivers/net/mlx5/mlx5_stats.c
+++ b/drivers/net/mlx5/mlx5_stats.c
@@ -3,11 +3,13 @@
  * Copyright 2015 Mellanox Technologies, Ltd
  */
 
+#include <fcntl.h>
 #include <inttypes.h>
 #include <linux/sockios.h>
 #include <linux/ethtool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <unistd.h>
 
 #include <rte_ethdev_driver.h>
 #include <rte_common.h>
@@ -142,20 +144,23 @@
 static inline void
 mlx5_read_ib_stat(struct mlx5_priv *priv, const char *ctr_name, uint64_t *stat)
 {
-	FILE *file;
+	int fd;
+
 	if (priv->sh) {
 		MKSTR(path, "%s/ports/%d/hw_counters/%s",
 			  priv->sh->ibdev_path,
 			  priv->ibv_port,
 			  ctr_name);
-
-		file = fopen(path, "rb");
-		if (file) {
-			int n = fscanf(file, "%" SCNu64, stat);
-
-			fclose(file);
-			if (n == 1)
+		fd = open(path, O_RDONLY);
+		if (fd != -1) {
+			char buf[21] = {'\0'};
+			ssize_t n = read(fd, buf, sizeof(buf));
+
+			close(fd);
+			if (n != -1) {
+				*stat = strtoull(buf, NULL, 10);
 				return;
+			}
 		}
 	}
 	*stat = 0;
-- 
1.8.3.1