[PATCH net-next v5 2/2] selftests/bpf: add a new test to check the consumer update case

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

The subtest sends 33 packets at one time on purpose to see if xsk
exitting __xsk_generic_xmit() updates the global consumer of tx queue
when reaching the max loop (max_tx_budget, 32 by default). The number 33
can avoid xskq_cons_peek_desc() updates the consumer when it's about to
quit sending, to accurately check if the issue that the first patch
resolves remains. The new case will not check this issue in zero copy
mode.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
v5
Link: https://lore.kernel.org/all/20250627085745.53173-1-kerneljasonxing@gmail.com/
1. use the initial approach to add a new testcase
2. add a new flag 'check_consumer' to see if the check is needed
---
 tools/testing/selftests/bpf/xskxceiver.c | 51 +++++++++++++++++++++++-
 tools/testing/selftests/bpf/xskxceiver.h |  1 +
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
index 0ced4026ee44..ed12a55ecf2a 100644
--- a/tools/testing/selftests/bpf/xskxceiver.c
+++ b/tools/testing/selftests/bpf/xskxceiver.c
@@ -109,6 +109,8 @@
 
 #include <network_helpers.h>
 
+#define MAX_TX_BUDGET_DEFAULT 32
+
 static bool opt_verbose;
 static bool opt_print_tests;
 static enum test_mode opt_mode = TEST_MODE_ALL;
@@ -1091,11 +1093,45 @@ static bool is_pkt_valid(struct pkt *pkt, void *buffer, u64 addr, u32 len)
 	return true;
 }
 
+static u32 load_value(u32 *counter)
+{
+	return __atomic_load_n(counter, __ATOMIC_ACQUIRE);
+}
+
+static bool kick_tx_with_check(struct xsk_socket_info *xsk, int *ret)
+{
+	u32 max_budget = MAX_TX_BUDGET_DEFAULT;
+	u32 cons, ready_to_send;
+	int delta;
+
+	cons = load_value(xsk->tx.consumer);
+	ready_to_send = load_value(xsk->tx.producer) - cons;
+	*ret = sendto(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, 0);
+
+	delta = load_value(xsk->tx.consumer) - cons;
+	/* By default, xsk should consume exact @max_budget descs at one
+	 * send in this case where hitting the max budget limit in while
+	 * loop is triggered in __xsk_generic_xmit(). Please make sure that
+	 * the number of descs to be sent is larger than @max_budget, or
+	 * else the tx.consumer will be updated in xskq_cons_peek_desc()
+	 * in time which hides the issue we try to verify.
+	 */
+	if (ready_to_send > max_budget && delta != max_budget)
+		return false;
+
+	return true;
+}
+
 static int kick_tx(struct xsk_socket_info *xsk)
 {
 	int ret;
 
-	ret = sendto(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, 0);
+	if (xsk->check_consumer) {
+		if (!kick_tx_with_check(xsk, &ret))
+			return TEST_FAILURE;
+	} else {
+		ret = sendto(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, 0);
+	}
 	if (ret >= 0)
 		return TEST_PASS;
 	if (errno == ENOBUFS || errno == EAGAIN || errno == EBUSY || errno == ENETDOWN) {
@@ -2613,6 +2649,18 @@ static int testapp_adjust_tail_grow_mb(struct test_spec *test)
 				   XSK_UMEM__LARGE_FRAME_SIZE * 2);
 }
 
+static int testapp_tx_queue_consumer(struct test_spec *test)
+{
+	int nr_packets = MAX_TX_BUDGET_DEFAULT + 1;
+
+	pkt_stream_replace(test, nr_packets, MIN_PKT_SIZE);
+	test->ifobj_tx->xsk->batch_size = nr_packets;
+	if (!(test->mode & TEST_MODE_ZC))
+		test->ifobj_tx->xsk->check_consumer = true;
+
+	return testapp_validate_traffic(test);
+}
+
 static void run_pkt_test(struct test_spec *test)
 {
 	int ret;
@@ -2723,6 +2771,7 @@ static const struct test_spec tests[] = {
 	{.name = "XDP_ADJUST_TAIL_SHRINK_MULTI_BUFF", .test_func = testapp_adjust_tail_shrink_mb},
 	{.name = "XDP_ADJUST_TAIL_GROW", .test_func = testapp_adjust_tail_grow},
 	{.name = "XDP_ADJUST_TAIL_GROW_MULTI_BUFF", .test_func = testapp_adjust_tail_grow_mb},
+	{.name = "TX_QUEUE_CONSUMER", .test_func = testapp_tx_queue_consumer},
 	};
 
 static void print_tests(void)
diff --git a/tools/testing/selftests/bpf/xskxceiver.h b/tools/testing/selftests/bpf/xskxceiver.h
index 67fc44b2813b..4df3a5d329ac 100644
--- a/tools/testing/selftests/bpf/xskxceiver.h
+++ b/tools/testing/selftests/bpf/xskxceiver.h
@@ -95,6 +95,7 @@ struct xsk_socket_info {
 	u32 batch_size;
 	u8 dst_mac[ETH_ALEN];
 	u8 src_mac[ETH_ALEN];
+	bool check_consumer;
 };
 
 struct pkt {
-- 
2.41.3