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net/mlx5: Read of "out_of_buffer" using fopen/fscanf/fclose causing TLB shootdowns due to mmap/munmap

dpdk-dev Mohsin Shaikh 1 participant 2 messages Apr 9, 2020 2 messages not in the archive Network drivers

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Mohsin Shaikh

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Hi Alexander,

Thank you for your quick response. Please find attached the patch for bug 440.

- Mohsin

Quoted 24 lines · On 9 Apr 2020, at 1:07 AM, [email protected] wrote:

https://bugs.dpdk.org/show_bug.cgi?id=440

Alexander Kozyrev ([email protected]) changed:

What |Removed |Added
----------------------------------------------------------------------------

    Ever confirmed|0                           |1
            Status|UNCONFIRMED                 |CONFIRMED
                CC|                            |[email protected]

--- Comment #1 from Alexander Kozyrev ([email protected]) --- Hi Mohsin, thank you for the problem description and especially for the patch. Would you mind sending this patch to DPDK mailing list so we can integrate it? The patch looks really good to me. The only small thing I would like to change. Could you please use SCNu64 macro instead of "%lu" in the sscanf function?
sscanf(buf, "%" SCNu64, stat);

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#3 lore raw

Resending.

============================================================
commit 89681d3655f27d758537ae01a02d500deee1acd6

Author: Mohsin Shaikh <[email protected]>
Date:   Thu Apr 9 12:19:45 2020 +0800

net/mlx5: Use open/read/close for reading ib stat

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.

The details can be found here:
https://bugs.dpdk.org/show_bug.cgi?id=440

Bugzilla ID: 440

drivers/net/mlx5/mlx5_stats.c +11 -7
index 205e4fe..91ac933 100644
@@ -8,6 +8,8 @@
 #include <linux/ethtool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
 
 #include <rte_ethdev_driver.h>
 #include <rte_common.h>

@@ -139,20 +141,22 @@
 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[32];
+			ssize_t n = read(fd, buf, sizeof(buf));
+			close(fd);
+			if (n != -1) {
+				sscanf(buf, "%" SCNu64, stat);
 				return;
+			}
 		}
 	}
 	*stat = 0;

============================================================

Thanks,
Mohsin

Quoted 33 lines · Mohsin Shaikh

Hi Alexander,

Thank you for your quick response. Please find attached the patch for bug 440.

- Mohsin

Quoted 22 lines · On 9 Apr 2020, at 1:07 AM, [email protected] wrote:

https://bugs.dpdk.org/show_bug.cgi?id=440

Alexander Kozyrev ([email protected]) changed:

What |Removed |Added
----------------------------------------------------------------------------

   Ever confirmed|0                           |1
           Status|UNCONFIRMED                 |CONFIRMED
               CC|                            |[email protected]

--- Comment #1 from Alexander Kozyrev ([email protected]) --- Hi Mohsin, thank you for the problem description and especially for the patch. Would you mind sending this patch to DPDK mailing list so we can integrate it? The patch looks really good to me. The only small thing I would like to change. Could you please use SCNu64 macro instead of "%lu" in the sscanf function?
sscanf(buf, "%" SCNu64, stat);

Signature · 2 lines
You are receiving this mail because:
You reported the bug.