[PATCH 0/3] net/9p: Add 9P transport over USB4STREAM

[Alan Borzeszkowski <alan.borzeszkowski@linux.intel.com>]

This series adds trans=thunderbolt, a 9P transport over the
Thunderbolt/USB4 DMA tunnels exposed by the tbstream character devices
(USB4STREAM). It's designed for simple host-to-host file sharing over
single Thunderbolt/USB4 cable.

Today the only practical way to use 9P over a USB4 link is trans=fd
which, due to its design, cannot fully utilize USB4STREAM capabilities.
Thunderbolt transport offers a simpler mount (no fd redirection required),
busy-poll support and substantial throughput increase compared to FD
transport.

User may mount 9P export with following command:

mount -t 9p -o trans=thunderbolt,aname=<exported_remote> /dev/tbstreamX /mnt

Thunderbolt transport achieves a median 1.21x more throughput compared
to FD transport under same conditions, and the advantage grows with
concurrency: 1.03-1.09x at 1-2 threads, 1.14-1.27x at 4, and 1.34-2.28x
at 8-16.

As an example, 4K random reads, 4 worker threads. FD transport achieves
~53k IOPS, Thunderbolt transport ~66k (+24.7%). 4K random writes follow:
FD ~28k IOPS, Thunderbolt ~33k (+19.4%).

With busy-poll enabled, throughput drastically increases for
single-threaded workloads. 4K random read, 1 thread: FD transport 12,345
IOPS, Thunderbolt 12,843 IOPS (+4%), Thunderbolt + busy-poll 22,262 IOPS
(+80.3% vs fd). Normally, busy-polling trades lower latency for increase
in CPU usage but measured system CPU usage was lower (23.1% -> 15.2%).

Above is replicated in more practical example: simulated file-manager
style copy (drag&drop in GUI) of extracted Chromium release repo. Copy
from 9P client to 9P server took 22m29s for FD transport, 21m52s for
Thunderbolt transport (-3%), 14m50s for Thunderbolt + busy-poll (-34%).

__Technical details__
'fio' based benchmarks: random read, random write
ioengine=psync, direct I/O, bs=512-128k, numjobs=1-16, rsize=128M,
runtime=60, ramp=5

'GUI' copy simulation: one extracted chromium-156.0.8066.9 release, 4126
MiB, cp -a --no-preserve=ownership.

Testing was done between two hosts over a single Thunderbolt 5 cable,
with diod as the server (version: 1.1.0-24-gde51d1e), fio (version:
3.36) on modified v7.3 kernel, Ubuntu 24.04 LTS.
Every transport ran on default settings: "msize=131096, cache=none,
version=9p2000.L". Each scenario result is 3-run median. Between each
run, 9P FS was remounted and page cache was dropped on both server and
client.

Alan Borzeszkowski (3):
  thunderbolt: stream: Add tbstream_dev_from_file()
  net/9p/thunderbolt: Add native 9P Thunderbolt transport support
  Documentation/fs/9p: Add Thunderbolt transport documentation

 Documentation/filesystems/9p.rst   |  39 +++-
 MAINTAINERS                        |   1 +
 drivers/thunderbolt/stream.c       |  16 ++
 include/linux/thunderbolt_stream.h |  14 ++
 net/9p/Kconfig                     |   7 +
 net/9p/Makefile                    |   4 +
 net/9p/trans_thunderbolt.c         | 348 +++++++++++++++++++++++++++++
 7 files changed, 419 insertions(+), 10 deletions(-)
 create mode 100644 include/linux/thunderbolt_stream.h
 create mode 100644 net/9p/trans_thunderbolt.c


base-commit: 93f51579e7df248780214094418f205253383cc5
-- 
2.53.0