uthread: add cooperative multi-tasking interface
Add a new internal API called uthread (Kconfig symbol: UTHREAD) which
provides cooperative multi-tasking. The goal is to be able to improve
the performance of some parts of U-Boot by overlapping lengthy
operations, and also implement background jobs in the U-Boot shell.
Each uthread has its own stack allocated on the heap. The default stack
size is defined by the UTHREAD_STACK_SIZE symbol and is used when
uthread_create() receives zero for the stack_sz argument.
The implementation is based on context-switching via initjmp()/setjmp()/
longjmp() and is inspired from barebox threads [1]. A notion of thread
group helps with dependencies, such as when a thread needs to block
until a number of other threads have returned.
The name "uthread" comes from "user-space threads" because the
scheduling happens with no help from a higher privileged mode, contrary
to more complex models where kernel threads are defined. But the 'u'
may as well stand for 'U-Boot' since the bootloader may actually be
running at any privilege level and the notion of user vs. kernel may
not make much sense in this context.
[1] https://github.com/barebox/barebox/blob/master/common/bthread.c
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/lib/Kconfig b/lib/Kconfig
index ac34ec4..b2aecd8 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -1258,6 +1258,27 @@
enable this config option to distinguish them using
phandles in fdtdec_get_alias_seq() function.
+config UTHREAD
+ bool "Enable thread support"
+ depends on HAVE_INITJMP
+ help
+ Implement a simple form of cooperative multi-tasking based on
+ context-switching via initjmp(), setjmp() and longjmp(). The
+ uthread_ interface enables the main thread of execution to create
+ one or more secondary threads and schedule them until they all have
+ returned. At any point a thread may suspend its execution and
+ schedule another thread, which allows for the efficient multiplexing
+ of leghthy operations.
+
+config UTHREAD_STACK_SIZE
+ int "Default uthread stack size"
+ depends on UTHREAD
+ default 32768
+ help
+ The default stack size for uthreads. Each uthread has its own stack.
+ When the stack_sz argument to uthread_create() is zero then this
+ value is used.
+
endmenu
source "lib/fwu_updates/Kconfig"