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[v5,00/16] Uthreads

Message ID 20250331123120.2025062-1-jerome.forissier@linaro.org
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Series Uthreads | expand

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Jerome Forissier March 31, 2025, 12:30 p.m. UTC 
This series introduces threads and uses them for two things:
- Improve the performance of the USB bus scanning code (scan multiple
busses simultaneously),
- Implement background jobs in the shell via two new commands: 'spawn'
and 'wait'.

The threading framework is called 'uthread' and is inspired from the
barebox threads [2]. setjmp() and longjmp() are used to save and
restore contexts, as well as a non-standard extension called initjmp().
This new function is added in several patches, one for each
architecture that supports HAVE_SETJMP. A new symbol is defined:
HAVE_INITJMP. Two tests, one for initjmp() and one for the uthread
scheduling, are added to the lib suite.

The schedule() and udelay() function are updated to become thread
re-scheduling points, and mutex objects are introduced. With that the
USB stack initialization is modified to benefit from concurrency when
UTHREAD is enabled, where uthreads are used in usb_init() to initialize
and scan multiple busses at the same time. The code was tested on arm64
and arm QEMU with 4 simulated XHCI buses and some devices. On this
platform the USB scan takes 2.2 s instead of 5.6 s. Tested on i.MX93 EVK
with two USB hubs, one ethernet adapter and one webcam on each, "usb
start" takes 2.4 s instead of 4.6 s.

Finally, the spawn and wait commands are introduced, allowing the use of
threads from the shell. Tested on the i.MX93 EVK with a spinning HDD
connected to USB1 and the network connected to ENET1. The USB plus DHCP
init sequence "spawn usb start; spawn dhcp; wait" takes 4.5 seconds
instead of 8 seconds for "usb start; dhcp".

[1] https://patchwork.ozlabs.org/project/uboot/list/?series=446674
[2] https://github.com/barebox/barebox/blob/master/common/bthread.c

Changes in v5:
- Rebase on top of next (at d5742298803 "Merge tag 'qcom-next-20250324'
of https://gitlab.denx.de/u-boot/custodians/u-boot-snapdragon into next")
- Apply review tags
- Explain why initjmp() is introduced for every platform (arm, riscv,
sandbox).
- Implement mutexes ("uthread: add uthread_mutex", "test: lib: add
uthread_mutex test")
- USB: keep 'controllers_initialized' local to usb_init() and use the DM
function device_active() to count the controllers initialized successfully.
Protect the USB devices with a mutex (so usb_init() cannot run concurrently
with usb_stop()).
- Fix copyright in cmd/spawn.c

Changes in v4:
- Rebase on top of next (at 5ca70325b64 "Merge branch 'fixes' of
https://source.denx.de/u-boot/custodians/u-boot-tegra into next")
- Add a stack_sz parameter to initjmp(). This is made necessary by the
sandbox implementation which relies on sigaltstack(), which need both
the stack base address and its size in its stack_t argument. In any
case it is cleaner to provide the exact stack boundaries. With that,
a crash was fixed on sandbox in the lib_initjmp unit test.
@Ilias: I kept your R-b on the two patches with a trivial change
(passing one more parameter), but I removed it from "arm: add initjmp()"
since there's one more line of assembly code and who knows what I might
have done wrong ;)
- Remove symbol UTHREAD_GRANULARITY and use a tight scheduling loop in
delay() instead. Tests on an i.MX93 board have shown that setting
UTHREAD_GRANULARITY as low as 10 microseconds (or higher) can have a
negative impact on the console input (some key presses do not register)
while 0 makes the console fully responsive.  The test consist in running
"spawn sleep 10" and typing a command. I suspect other platforms may
behave similarly, therefore do not bother with the added complexity of
a configurable delay.
- Apply review tags

Changes in v3:
- Rebase on top of Heinrich's series "common: cleanup usage of structure
jmp_buf_data":
https://patchwork.ozlabs.org/project/uboot/list/?series=446674
https://lists.denx.de/pipermail/u-boot/2025-March/582221.html
- HAVE_INITJMP now depends on HAVE_SETJMP. Provide proper Sphinx-like
documentaion for initjmp().
- test/lib/initjmp.c: change SPDX license tag from GPL2.0+ to
GPL-2.0-or-later
- Add doc/api/setjmp.rst. The initjmp() test is used as an example in the
documentation.
- uthread_create() now accepts an optional user-allocated struct uthread
- Remove the list_empty() test from uthread_schedule() (not needed)
- Add Sphinx doc to all functions in uthread.h (moved from uthread.c).
- Add doc/api/uthread.rst. The uthread test is used as an example in the
documentation.
- Document struct uthread and its components
- Provide numbers to justify the scheduling loop in udelay() in commit
"lib: time: hook uthread_schedule() into udelay()".
- Do not insert uthread_schedule() in common/console.c:fgetc() since it
is already in schedule()
- The wait command can be interrupted with Ctrl-C
- Switch spawn and wait tests from DM_TEST() to CMD_TEST()
- Add MAINTAINERS entry
- Apply review tags

Changes in v2:
- Rewrite the cover letter, do not mention the older coroutines series
- Rebased onto next
- UTHREAD_STACK_SIZE is set to 32768 (32 KiB) instead of 32178
- Remove uthread_free_all() and let threads be freed as they terminate
by uthread_schedule()
- Add function descriptions
- Add documentation (doc/develop/uthread.rst)
- Explain initjmp() in the description of "arch: introduce symbol
HAVE_INITJMP".
- Add thread groups (uthread_grp_new_id() and uthread_grp_done())
- Add the spawn and wait commands

Jerome Forissier (16):
  arch: introduce initjmp() and Kconfig symbol HAVE_INITJMP
  arm: add initjmp()
  riscv: add initjmp()
  sandbox: add initjmp()
  test: lib: add initjmp() test
  uthread: add cooperative multi-tasking interface
  uthread: add uthread_mutex
  cyclic: invoke uthread_schedule() from schedule()
  lib: time: hook uthread_schedule() into udelay()
  test: lib: add uthread test
  test: lib: add uthread_mutex test
  dm: usb: move bus initialization into new static function
    usb_init_bus()
  dm: usb: initialize and scan multiple buses simultaneously with
    uthread
  cmd: add spawn and wait commands
  test: cmd: add test for spawn and wait commands
  MAINTAINERS: add UTHREAD

 MAINTAINERS                   |   9 ++
 arch/Kconfig                  |   9 ++
 arch/arm/lib/setjmp.S         |  12 +++
 arch/arm/lib/setjmp_aarch64.S |  10 ++
 arch/riscv/lib/setjmp.S       |  11 ++
 arch/sandbox/cpu/Makefile     |  11 +-
 arch/sandbox/cpu/initjmp.c    | 175 +++++++++++++++++++++++++++++++
 cmd/Kconfig                   |  17 +++
 cmd/Makefile                  |   2 +
 cmd/spawn.c                   | 188 +++++++++++++++++++++++++++++++++
 common/cyclic.c               |   3 +
 doc/api/index.rst             |   2 +
 doc/api/setjmp.rst            |  20 ++++
 doc/api/uthread.rst           |  19 ++++
 drivers/usb/host/usb-uclass.c | 192 ++++++++++++++++++++++++----------
 include/setjmp.h              |  32 ++++++
 include/u-boot/schedule.h     |   3 +
 include/uthread.h             | 183 ++++++++++++++++++++++++++++++++
 lib/Kconfig                   |  21 ++++
 lib/Makefile                  |   2 +
 lib/time.c                    |   9 +-
 lib/uthread.c                 | 166 +++++++++++++++++++++++++++++
 test/boot/bootdev.c           |  14 +--
 test/boot/bootflow.c          |   2 +-
 test/cmd/Makefile             |   1 +
 test/cmd/spawn.c              |  32 ++++++
 test/lib/Makefile             |   2 +
 test/lib/initjmp.c            |  73 +++++++++++++
 test/lib/uthread.c            | 146 ++++++++++++++++++++++++++
 29 files changed, 1303 insertions(+), 63 deletions(-)
 create mode 100644 arch/sandbox/cpu/initjmp.c
 create mode 100644 cmd/spawn.c
 create mode 100644 doc/api/setjmp.rst
 create mode 100644 doc/api/uthread.rst
 create mode 100644 include/uthread.h
 create mode 100644 lib/uthread.c
 create mode 100644 test/cmd/spawn.c
 create mode 100644 test/lib/initjmp.c
 create mode 100644 test/lib/uthread.c