Merge branch 'add-tso-map-once-dma-helpers-and-bnxt-sw-uso-support'

Joe Damato says:

====================
Add TSO map-once DMA helpers and bnxt SW USO support

Greetings:

This series extends net/tso to add a data structure and some helpers allowing
drivers to DMA map headers and packet payloads a single time. The helpers can
then be used to reference slices of shared mapping for each segment. This
helps to avoid the cost of repeated DMA mappings, especially on systems which
use an IOMMU. N per-packet DMA maps are replaced with a single map for the
entire GSO skb. As of v3, the series uses the DMA IOVA API (as suggested by
Leon [1]) and provides a fallback path when an IOMMU is not in use. The DMA
IOVA API provides even better efficiency than the v2; see below.

The added helpers are then used in bnxt to add support for software UDP
Segmentation Offloading (SW USO) for older bnxt devices which do not have
support for USO in hardware. Since the helpers are generic, other drivers
can be extended similarly.

The v2 showed a ~4x reduction in DMA mapping calls at the same wire packet
rate on production traffic with a bnxt device. The v3, however, shows a larger
reduction of about ~6x at the same wire packet rate. This is thanks to Leon's
suggestion of using the DMA IOVA API [1].

Special care is taken to make bnxt ethtool operations work correctly: the ring
size cannot be reduced below a minimum threshold while USO is enabled and
growing the ring automatically re-enables USO if it was previously blocked.

This v10 contains some cosmetic changes (wrapping long lines), moves the test
to the correct directory, and attempts to fix the slot availability check
added in the v9.

I re-ran the python test and the test passed on my bnxt system. I also ran
this on a production system.
====================

Link: https://patch.msgid.link/20260408230607.2019402-1-joe@dama.to
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 104 insertions, 0 deletions

diff --git a/tools/testing/selftests/drivers/net/hw/Makefile b/tools/testing/selftests/drivers/net/hw/Makefile
index d84e955ac87b..85ca4d1ecf9e 100644
--- a/tools/testing/selftests/drivers/net/hw/Makefile
+++ b/tools/testing/selftests/drivers/net/hw/Makefile
@@ -45,6 +45,7 @@ TEST_PROGS = \
 	rss_input_xfrm.py \
 	toeplitz.py \
 	tso.py \
+	uso.py \
 	xdp_metadata.py \
 	xsk_reconfig.py \
 	#
diff --git a/tools/testing/selftests/drivers/net/hw/uso.py b/tools/testing/selftests/drivers/net/hw/uso.py
new file mode 100755
index 000000000000..6d61e56cab3c
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/hw/uso.py
@@ -0,0 +1,103 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+"""Test USO
+
+Sends large UDP datagrams with UDP_SEGMENT and verifies that the peer
+receives the expected total payload and that the NIC transmitted at least
+the expected number of segments.
+"""
+import random
+import socket
+import string
+
+from lib.py import ksft_run, ksft_exit, KsftSkipEx
+from lib.py import ksft_eq, ksft_ge, ksft_variants, KsftNamedVariant
+from lib.py import NetDrvEpEnv
+from lib.py import bkg, defer, ethtool, ip, rand_port, wait_port_listen
+
+# python doesn't expose this constant, so we need to hardcode it to enable UDP
+# segmentation for large payloads
+UDP_SEGMENT = 103
+
+
+def _send_uso(cfg, ipver, mss, total_payload, port):
+    if ipver == "4":
+        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        dst = (cfg.remote_addr_v["4"], port)
+    else:
+        sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+        dst = (cfg.remote_addr_v["6"], port)
+
+    sock.setsockopt(socket.IPPROTO_UDP, UDP_SEGMENT, mss)
+    payload = ''.join(random.choice(string.ascii_lowercase)
+                      for _ in range(total_payload))
+    sock.sendto(payload.encode(), dst)
+    sock.close()
+
+
+def _get_tx_packets(cfg):
+    stats = ip(f"-s link show dev {cfg.ifname}", json=True)[0]
+    return stats['stats64']['tx']['packets']
+
+
+def _test_uso(cfg, ipver, mss, total_payload):
+    cfg.require_ipver(ipver)
+    cfg.require_cmd("socat", remote=True)
+
+    features = ethtool(f"-k {cfg.ifname}", json=True)
+    uso_was_on = features[0]["tx-udp-segmentation"]["active"]
+
+    try:
+        ethtool(f"-K {cfg.ifname} tx-udp-segmentation on")
+    except Exception as exc:
+        raise KsftSkipEx(
+            "Device does not support tx-udp-segmentation") from exc
+    if not uso_was_on:
+        defer(ethtool, f"-K {cfg.ifname} tx-udp-segmentation off")
+
+    expected_segs = (total_payload + mss - 1) // mss
+
+    port = rand_port(stype=socket.SOCK_DGRAM)
+    rx_cmd = f"socat -{ipver} -T 2 -u UDP-LISTEN:{port},reuseport STDOUT"
+
+    tx_before = _get_tx_packets(cfg)
+
+    with bkg(rx_cmd, host=cfg.remote, exit_wait=True) as rx:
+        wait_port_listen(port, proto="udp", host=cfg.remote)
+        _send_uso(cfg, ipver, mss, total_payload, port)
+
+    ksft_eq(len(rx.stdout), total_payload,
+            comment=f"Received {len(rx.stdout)}B, expected {total_payload}B")
+
+    cfg.wait_hw_stats_settle()
+
+    tx_after = _get_tx_packets(cfg)
+    tx_delta = tx_after - tx_before
+
+    ksft_ge(tx_delta, expected_segs,
+            comment=f"Expected >= {expected_segs} tx packets, got {tx_delta}")
+
+
+def _uso_variants():
+    for ipver in ["4", "6"]:
+        yield KsftNamedVariant(f"v{ipver}_partial", ipver, 1400, 1400 * 10 + 500)
+        yield KsftNamedVariant(f"v{ipver}_exact", ipver, 1400, 1400 * 5)
+
+
+@ksft_variants(_uso_variants())
+def test_uso(cfg, ipver, mss, total_payload):
+    """Send a USO datagram and verify the peer receives the expected segments."""
+    _test_uso(cfg, ipver, mss, total_payload)
+
+
+def main() -> None:
+    """Run USO tests."""
+    with NetDrvEpEnv(__file__) as cfg:
+        ksft_run([test_uso],
+                 args=(cfg, ))
+    ksft_exit()
+
+
+if __name__ == "__main__":
+    main()