Stanislav Fomichev [off-list ref] writes:

+static int rxq_num(const char *ifname)
+{
+	struct ethtool_channels ch = {
+		.cmd = ETHTOOL_GCHANNELS,
+	};
+
+	struct ifreq ifr = {
+		.ifr_data = (void *)&ch,
+	};
+	strcpy(ifr.ifr_name, ifname);
+	int fd, ret;
+
+	fd = socket(AF_UNIX, SOCK_DGRAM, 0);
+	if (fd < 0)
+		error(-1, errno, "socket");
+
+	ret = ioctl(fd, SIOCETHTOOL, &ifr);
+	if (ret < 0)
+		error(-1, errno, "socket");
+
+	close(fd);
+
+	return ch.rx_count;
+}

mlx5 uses 'combined' channels, so this returns 0. Changing it to just:

return ch.rx_count ?: ch.combined_count; 

works though :)

-Toke