[PATCH v4 00/14] Uthreads
Jerome Forissier
jerome.forissier at linaro.org
Tue Mar 18 11:46:36 CET 2025
This series introduces threads and uses them to improve the performance
of the USB bus scanning code and to 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.
After introducing threads and making schedule() and udelay() a thread
re-scheduling point, 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 v4:
- Rebase on top of next (at 0e1fc465fea "Merge tag 'dm-pull-15mar25' of
git://git.denx.de/u-boot-dm 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 (14):
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
cyclic: invoke uthread_schedule() from schedule()
lib: time: hook uthread_schedule() into udelay()
test: lib: add uthread 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 | 168 +++++++++++++++++++++---------
include/setjmp.h | 32 ++++++
include/u-boot/schedule.h | 3 +
include/uthread.h | 123 ++++++++++++++++++++++
lib/Kconfig | 21 ++++
lib/Makefile | 2 +
lib/time.c | 9 +-
lib/uthread.c | 139 +++++++++++++++++++++++++
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 | 80 +++++++++++++++
29 files changed, 1128 insertions(+), 61 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
--
2.43.0
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