On 3/9/2021 10:19 AM, Ciara Loftus wrote:

This commit introduces support for preferred busy polling
to the AF_XDP PMD. This feature aims to improve single-core
performance for AF_XDP sockets under heavy load.

A new vdev arg is introduced called 'busy_budget' whose default
value is 64. busy_budget is the value supplied to the kernel
with the SO_BUSY_POLL_BUDGET socket option and represents the
busy-polling NAPI budget. To set the budget to a different value
eg. 256:

--vdev=net_af_xdp0,iface=eth0,busy_budget=256

Preferred busy polling is enabled by default provided a kernel with
version >= v5.11 is in use. To disable it, set the budget to zero.

The following settings are also strongly recommended to be used in
conjunction with this feature:

echo 2 | sudo tee /sys/class/net/eth0/napi_defer_hard_irqs
echo 200000 | sudo tee /sys/class/net/eth0/gro_flush_timeout

.. where eth0 is the interface being used by the PMD.

Signed-off-by: Ciara Loftus <redacted>

<...>

Can you please move the update after above the testpmd updates?
For more details the expected order is in the section comment.

+static int
+configure_preferred_busy_poll(struct pkt_rx_queue *rxq)
+{
+	int sock_opt = 1;
+	int fd = xsk_socket__fd(rxq->xsk);
+	int ret = 0;
+
+	ret = setsockopt(fd, SOL_SOCKET, SO_PREFER_BUSY_POLL,
+			(void *)&sock_opt, sizeof(sock_opt));
+	if (ret < 0) {
+		AF_XDP_LOG(DEBUG, "Failed to set SO_PREFER_BUSY_POLL\n");
+		goto err_prefer;
+	}
+
+	sock_opt = ETH_AF_XDP_DFLT_BUSY_TIMEOUT;
+	ret = setsockopt(fd, SOL_SOCKET, SO_BUSY_POLL, (void *)&sock_opt,
+			sizeof(sock_opt));
+	if (ret < 0) {
+		AF_XDP_LOG(DEBUG, "Failed to set SO_BUSY_POLL\n");

[1]

+		goto err_timeout;
+	}
+
+	sock_opt = rxq->busy_budget;
+	ret = setsockopt(fd, SOL_SOCKET, SO_BUSY_POLL_BUDGET,
+			(void *)&sock_opt, sizeof(sock_opt));
+	if (ret < 0) {
+		AF_XDP_LOG(DEBUG, "Failed to set SO_BUSY_POLL_BUDGET\n");

In above [1] and here, shouldn't the function return error, even the rollback is 
successful.
I am thinking a case an invalid 'busy_budget' provided, like a very big number 
or negative value.

+	} else {
+		AF_XDP_LOG(INFO, "Busy polling budget set to: %u\n",
+					rxq->busy_budget);
+		return 0;
+	}
+
+	/* setsockopt failure - attempt to restore xsk to default state and
+	 * proceed without busy polling support.
+	 */
+	sock_opt = 0;
+	ret = setsockopt(fd, SOL_SOCKET, SO_BUSY_POLL, (void *)&sock_opt,
+			sizeof(sock_opt));
+	if (ret < 0) {
+		AF_XDP_LOG(ERR, "Failed to unset SO_BUSY_POLL\n");
+		return -1;
+	}
+
+err_timeout:
+	sock_opt = 0;
+	ret = setsockopt(fd, SOL_SOCKET, SO_PREFER_BUSY_POLL,
+			(void *)&sock_opt, sizeof(sock_opt));
+	if (ret < 0) {
+		AF_XDP_LOG(ERR, "Failed to unset SO_PREFER_BUSY_POLL\n");
+		return -1;
+	}
+
+err_prefer:
+	rxq->busy_budget = 0;
+	return 0;
+}
+

<...>