[PATCH 5/5] selftests: iou-zcrx: add notification and stats test for zcrx

Clément Léger
2026-04-22T11:30:22Z

Add a selftest to verify that ZCRX notification are properly delivered
to userspace and that the shared-memory notification stats (copy_count,
copy_bytes) are correctly incremented when zero-copy RX falls back to
copying or when it runs out of buffers.

The test registers a notification descriptor during
IORING_REGISTER_ZCRX_IFQ with a stats region placed after the refill
queue entries. A new -n flag verifies that the copy fallback is
triggered and -b/-a flags allows to check for out of buffer
notification.

To reliably trigger copy fallback, the Python test uses a new
single_no_flow() setup variant that configures tcp-data-split and RSS
but without ethtool flow rule. Without flow steering, traffic arrives
on non-zcrx queues as regular pages, forcing the kernel copy-fallback
path in io_zcrx_copy_frag().

Out-of-buffer notification is verified by using a smaller receive area
and by avoiding recycling the buffers so that the kernel runs out of
buffer quickly.

Signed-off-by: Clément Léger <cleger@meta.com>
---
.../selftests/drivers/net/hw/iou-zcrx.c | 112 ++++++++++++++++--
.../selftests/drivers/net/hw/iou-zcrx.py | 49 +++++++-
2 files changed, 149 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/hw/iou-zcrx.c b/tools/testing/selftests/drivers/net/hw/iou-zcrx.c
index 240d13dbc54e..3c95e6460c24 100644
--- a/tools/testing/selftests/drivers/net/hw/iou-zcrx.c
+++ b/tools/testing/selftests/drivers/net/hw/iou-zcrx.c
@@ -52,7 +52,27 @@ struct t_io_uring_zcrx_ifq_reg {
struct io_uring_zcrx_offsets offsets;
__u32 zcrx_id;
__u32 rx_buf_len;
- __u64 __resv[3];
+ __u64 notif_desc;
+ __u64 __resv[2];
+};
+
+#define ZCRX_NOTIF_NO_BUFFERS (1 << 0)
+#define ZCRX_NOTIF_COPY (1 << 1)
+#define ZCRX_NOTIF_DESC_FLAG_STATS (1 << 0)
+
+#define NOTIF_USER_DATA 3
+
+struct t_zcrx_notification_desc {
+ __u64 user_data;
+ __u32 type_mask;
+ __u32 flags;
+ __u64 stats_offset;
+ __u64 __resv2[9];
+};
+
+struct t_io_uring_zcrx_notif_stats {
+ __u64 copy_count;
+ __u64 copy_bytes;
};

static long page_size;
@@ -84,7 +104,10 @@ static int cfg_oneshot_recvs;
static int cfg_send_size = SEND_SIZE;
static struct sockaddr_in6 cfg_addr;
static unsigned int cfg_rx_buf_len;
+static size_t cfg_area_size;
static bool cfg_dry_run;
+static bool cfg_copy_fallback;
+static bool cfg_no_buffers;

static char *payload;
static void *area_ptr;
@@ -95,6 +118,8 @@ static unsigned long area_token;
static int connfd;
static bool stop;
static size_t received;
+static unsigned int notif_received_mask;
+static size_t notif_stats_offset;

static unsigned long gettimeofday_ms(void)
{
@@ -142,6 +167,7 @@ static void setup_zcrx(struct io_uring *ring)
{
unsigned int ifindex;
unsigned int rq_entries = 4096;
+ size_t area_size = cfg_area_size ? cfg_area_size : AREA_SIZE;
int ret;

ifindex = if_nametoindex(cfg_ifname);
@@ -150,7 +176,7 @@ static void setup_zcrx(struct io_uring *ring)

if (cfg_rx_buf_len && cfg_rx_buf_len != page_size) {
area_ptr = mmap(NULL,
- AREA_SIZE,
+ area_size,
PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE |
MAP_HUGETLB | MAP_HUGE_2MB,
@@ -162,7 +188,7 @@ static void setup_zcrx(struct io_uring *ring)
}
} else {
area_ptr = mmap(NULL,
- AREA_SIZE,
+ area_size,
PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE,
0,
@@ -172,6 +198,12 @@ static void setup_zcrx(struct io_uring *ring)
}

ring_size = get_refill_ring_size(rq_entries);
+
+ if (cfg_copy_fallback) {
+ notif_stats_offset = ring_size;
+ ring_size += ALIGN_UP(sizeof(struct t_io_uring_zcrx_notif_stats), page_size);
+ }
+
ring_ptr = mmap(NULL,
ring_size,
PROT_READ | PROT_WRITE,
@@ -187,10 +219,11 @@ static void setup_zcrx(struct io_uring *ring)

struct io_uring_zcrx_area_reg area_reg = {
.addr = (__u64)(unsigned long)area_ptr,
- .len = AREA_SIZE,
+ .len = area_size,
.flags = 0,
};

+ struct t_zcrx_notification_desc notif_desc;
struct t_io_uring_zcrx_ifq_reg reg = {
.if_idx = ifindex,
.if_rxq = cfg_queue_id,
@@ -200,11 +233,32 @@ static void setup_zcrx(struct io_uring *ring)
.rx_buf_len = cfg_rx_buf_len,
};

+ if (cfg_copy_fallback || cfg_no_buffers) {
+ __u32 type_mask = 0;
+
+ if (cfg_copy_fallback)
+ type_mask = ZCRX_NOTIF_COPY;
+ if (cfg_no_buffers)
+ type_mask = ZCRX_NOTIF_NO_BUFFERS;
+
+ memset(&notif_desc, 0, sizeof(notif_desc));
+ notif_desc.user_data = NOTIF_USER_DATA;
+ notif_desc.type_mask = type_mask;
+ if (cfg_copy_fallback) {
+ notif_desc.flags = ZCRX_NOTIF_DESC_FLAG_STATS;
+ notif_desc.stats_offset = notif_stats_offset;
+ }
+ reg.notif_desc = (__u64)(unsigned long)&notif_desc;
+ }
+
ret = io_uring_register_ifq(ring, (void *)&reg);
if (cfg_rx_buf_len && (ret == -EINVAL || ret == -EOPNOTSUPP ||
ret == -ERANGE)) {
printf("Large chunks are not supported %i\n", ret);
exit(SKIP_CODE);
+ } else if ((cfg_copy_fallback || cfg_no_buffers) && ret == -EINVAL) {
+ printf("Notifications not supported %i\n", ret);
+ exit(SKIP_CODE);
} else if (ret) {
error(1, 0, "io_uring_register_ifq(): %d", ret);
}
@@ -304,10 +358,13 @@ static void process_recvzc(struct io_uring *ring, struct io_uring_cqe *cqe)
}
received += n;

- rqe = &rq_ring.rqes[(rq_ring.rq_tail & rq_mask)];
- rqe->off = (rcqe->off & ~IORING_ZCRX_AREA_MASK) | area_token;
- rqe->len = cqe->res;
- io_uring_smp_store_release(rq_ring.ktail, ++rq_ring.rq_tail);
+ /* Skip ring refill so that we ran out of buffers quickly */
+ if (!cfg_no_buffers) {
+ rqe = &rq_ring.rqes[(rq_ring.rq_tail & rq_mask)];
+ rqe->off = (rcqe->off & ~IORING_ZCRX_AREA_MASK) | area_token;
+ rqe->len = cqe->res;
+ io_uring_smp_store_release(rq_ring.ktail, ++rq_ring.rq_tail);
+ }
}

static void server_loop(struct io_uring *ring)
@@ -324,8 +381,15 @@ static void server_loop(struct io_uring *ring)
process_accept(ring, cqe);
else if (cqe->user_data == 2)
process_recvzc(ring, cqe);
- else
+ else if ((cfg_copy_fallback || cfg_no_buffers) &&
+ cqe->user_data == NOTIF_USER_DATA) {
+ notif_received_mask |= cqe->res;
+ if (cfg_no_buffers &&
+ (cqe->res & ZCRX_NOTIF_NO_BUFFERS))
+ stop = true;
+ } else {
error(1, 0, "unknown cqe");
+ }
count++;
}
io_uring_cq_advance(ring, count);
@@ -374,6 +438,23 @@ static void run_server(void)

if (!stop)
error(1, 0, "test failed\n");
+
+ if (cfg_copy_fallback) {
+ struct t_io_uring_zcrx_notif_stats *stats =
+ (void *)((char *)ring_ptr + notif_stats_offset);
+
+ if (!(notif_received_mask & ZCRX_NOTIF_COPY))
+ error(1, 0, "expected copy fallback notification");
+ if (!IO_URING_READ_ONCE(stats->copy_count))
+ error(1, 0, "expected copy_count > 0");
+ if (!IO_URING_READ_ONCE(stats->copy_bytes))
+ error(1, 0, "expected copy_bytes > 0");
+ }
+
+ if (cfg_no_buffers) {
+ if (!(notif_received_mask & ZCRX_NOTIF_NO_BUFFERS))
+ error(1, 0, "expected no-buffers notification");
+ }
}

static void run_client(void)
@@ -425,7 +506,7 @@ static void parse_opts(int argc, char **argv)
usage(argv[0]);
cfg_payload_len = max_payload_len;

- while ((c = getopt(argc, argv, "sch:p:l:i:q:o:z:x:d")) != -1) {
+ while ((c = getopt(argc, argv, "sch:p:l:i:q:o:z:x:a:dnb")) != -1) {
switch (c) {
case 's':
if (cfg_client)
@@ -466,8 +547,19 @@ static void parse_opts(int argc, char **argv)
case 'd':
cfg_dry_run = true;
break;
+ case 'n':
+ cfg_copy_fallback = true;
+ break;
+ case 'b':
+ cfg_no_buffers = true;
+ break;
+ case 'a':
+ cfg_area_size = strtoul(optarg, NULL, 0) * page_size;
+ break;
}
}
+ if (cfg_copy_fallback && cfg_no_buffers)
+ error(1, 0, "Pass one of -n or -b");

if (cfg_server && addr)
error(1, 0, "Receiver cannot have -h specified");
diff --git a/tools/testing/selftests/drivers/net/hw/iou-zcrx.py b/tools/testing/selftests/drivers/net/hw/iou-zcrx.py
index e81724cb5542..f7f1cbff5959 100755
--- a/tools/testing/selftests/drivers/net/hw/iou-zcrx.py
+++ b/tools/testing/selftests/drivers/net/hw/iou-zcrx.py
@@ -41,7 +41,9 @@ def set_flow_rule_rss(cfg, rss_ctx_id):
return int(values)

-def single(cfg):
+def single_no_flow(cfg):
+ """Like single() but without a flow rule."""
+
channels = cfg.ethnl.channels_get({'header': {'dev-index': cfg.ifindex}})
channels = channels['combined-count']
if channels < 2:
@@ -65,6 +67,9 @@ def single(cfg):
ethtool(f"-X {cfg.ifname} equal {cfg.target}")
defer(ethtool, f"-X {cfg.ifname} default")

+def single(cfg):
+ single_no_flow(cfg)
+
flow_rule_id = set_flow_rule(cfg)
defer(ethtool, f"-N {cfg.ifname} delete {flow_rule_id}")

@@ -130,6 +135,26 @@ def test_zcrx_oneshot(cfg, setup) -> None:
cmd(tx_cmd, host=cfg.remote)

+@ksft_variants([
+ KsftNamedVariant("single", single_no_flow),
+])
+def test_zcrx_notif(cfg, setup) -> None:
+ """Test zcrx copy fallback notification.
+
+ Omits the flow rule so traffic arrives on non-zcrx queues as regular
+ pages, forcing the kernel copy-fallback path. Asserts that the
+ ZCRX_NOTIF_COPY notification CQE is delivered."""
+
+ cfg.require_ipver('6')
+
+ setup(cfg)
+ rx_cmd = f"{cfg.bin_local} -s -p {cfg.port} -i {cfg.ifname} -q {cfg.target} -n"
+ tx_cmd = f"{cfg.bin_remote} -c -h {cfg.addr_v['6']} -p {cfg.port} -l 12840"
+ with bkg(rx_cmd, exit_wait=True):
+ wait_port_listen(cfg.port, proto="tcp")
+ cmd(tx_cmd, host=cfg.remote)
+
+
def test_zcrx_large_chunks(cfg) -> None:
"""Test zcrx with large buffer chunks."""

@@ -157,6 +182,25 @@ def test_zcrx_large_chunks(cfg) -> None:
cmd(tx_cmd, host=cfg.remote)

+@ksft_variants([
+ KsftNamedVariant("single", single),
+])
+def test_zcrx_notif_no_buffers(cfg, setup) -> None:
+ """Test zcrx out-of-buffer notification.
+
+ Skips buffer refill so the pool is quickly exhausted, triggering
+ a ZCRX_NOTIF_NO_BUFFERS notification CQE."""
+
+ cfg.require_ipver('6')
+
+ setup(cfg)
+ rx_cmd = f"{cfg.bin_local} -s -p {cfg.port} -i {cfg.ifname} -q {cfg.target} -b -a 64"
+ tx_cmd = f"{cfg.bin_remote} -c -h {cfg.addr_v['6']} -p {cfg.port} -l 12840"
+ with bkg(rx_cmd, exit_wait=True):
+ wait_port_listen(cfg.port, proto="tcp")
+ cmd(tx_cmd, host=cfg.remote, fail=False)
+
+
def main() -> None:
with NetDrvEpEnv(__file__) as cfg:
cfg.bin_local = path.abspath(path.dirname(__file__) + "/../../../drivers/net/hw/iou-zcrx")
@@ -166,7 +210,8 @@ def main() -> None:
cfg.netnl = NetdevFamily()
cfg.port = rand_port()
ksft_run(globs=globals(), cases=[test_zcrx, test_zcrx_oneshot,
- test_zcrx_large_chunks], args=(cfg, ))
+ test_zcrx_large_chunks, test_zcrx_notif,
+ test_zcrx_notif_no_buffers], args=(cfg, ))
ksft_exit()

--
2.52.0