kernel: system workqueue stack size as maximum

doc/kernel/services/threads/workqueue.rst

@@ -215,6 +215,23 @@ use of it.
     for example, if the new work items perform blocking operations that
     would delay other system workqueue processing to an unacceptable degree.
 
+Stack Size
+==========
+
+By default the stack size of the system workqueue is determined co-operatively
+among all users of the workqueue. The build system compares the value of all
+Kconfig symbols matching the pattern
+``CONFIG_SYSTEM_WORKQUEUE_MIN_STACK_SIZE_*`` and selects the largest value as
+the stack size. :kconfig:option:`CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE` is
+included in this calculation by its value being copied into
+:kconfig:option:`CONFIG_SYSTEM_WORKQUEUE_MIN_STACK_SIZE_DEFAULT`.
+
+.. note::
+    This behaviour can be disabled through
+    :kconfig:option:`CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE_IGNORE_MIN`, in which
+    case the value of :kconfig:option:`CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE` will
+    be used directly.
+
 How to Use Workqueues
 *********************
 

doc/releases/migration-guide-4.2.rst

@@ -26,6 +26,15 @@ Build System
 Kernel
 ******
 
+* The stack size of the system workqueue is now computed co-operatively
+  among users as the maximum value of any Kconfig options whose name starts
+  with ``CONFIG_SYSTEM_WORKQUEUE_MIN_STACK_SIZE_``. The existing
+  :kconfig:option:`CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE` symbol value is copied
+  to :kconfig:option:`CONFIG_SYSTEM_WORKQUEUE_MIN_STACK_SIZE_DEFAULT` so that
+  it is included in the calculation without any application changes.
+  The previous behaviour can be selected with
+  :kconfig:option:`CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE_IGNORE_MIN`.
+
 Boards
 ******
 

kernel/CMakeLists.txt

@@ -193,6 +193,21 @@ if(${CONFIG_KERNEL_MEM_POOL})
   zephyr_compile_definitions(K_HEAP_MEM_POOL_SIZE=${final_heap_size})
 endif()
 
+# Import all custom SYSTEM_WORKQUEUE_MIN_STACK_SIZE size requirements
+import_kconfig(CONFIG_SYSTEM_WORKQUEUE_MIN_STACK_SIZE_ ${DOTCONFIG} min_stack_size_keys)
+if(${CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE_IGNORE_MIN})
+  set(stack_size_max ${CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE})
+else()
+  # Find the largest of all "MIN_STACK_SIZE" requested
+  set(stack_size_max 0)
+  foreach(val ${min_stack_size_keys})
+    if(${${val}} GREATER ${stack_size_max})
+      set(stack_size_max ${${val}})
+    endif()
+  endforeach()
+endif()
+zephyr_compile_definitions(K_SYSTEM_WORKQUEUE_STACK_SIZE=${stack_size_max})
+
 # The last 2 files inside the target_sources_ifdef should be
 # userspace_handler.c and userspace.c. If not the linker would complain.
 # This order has to be maintained. Any new file should be placed

kernel/Kconfig

@@ -577,10 +577,23 @@ rsource "Kconfig.obj_core"
 menu "System Work Queue Options"
 config SYSTEM_WORKQUEUE_STACK_SIZE
 	int "System workqueue stack size"
-	default 4096 if COVERAGE_GCOV
-	default 2560 if WIFI_NM_WPA_SUPPLICANT
 	default 1024
 
+config SYSTEM_WORKQUEUE_STACK_SIZE_IGNORE_MIN
+	bool "Ignore the minimum system workqueue stack size requirement"
+	help
+	  This option can be set to force setting a smaller system workqueue
+	  stack size than what's specified by enabled subsystems. This can be
+	  useful when optimizing memory usage and a more precise system workqueue
+	  size is known for a given application.
+
+
+config SYSTEM_WORKQUEUE_MIN_STACK_SIZE_DEFAULT
+	int
+	default SYSTEM_WORKQUEUE_STACK_SIZE
+	help
+	  Used to maintain compatibility with explicit stack size setting.
+
 config SYSTEM_WORKQUEUE_PRIORITY
 	int "System workqueue priority"
 	default -2 if COOP_ENABLED && !PREEMPT_ENABLED

kernel/system_work_q.c

@@ -14,8 +14,7 @@
 #include <zephyr/kernel.h>
 #include <zephyr/init.h>
 
-static K_KERNEL_STACK_DEFINE(sys_work_q_stack,
-			     CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE);
+static K_KERNEL_STACK_DEFINE(sys_work_q_stack, K_SYSTEM_WORKQUEUE_STACK_SIZE);
 
 struct k_work_q k_sys_work_q;
 

modules/hostap/Kconfig

@@ -22,6 +22,10 @@ config WIFI_NM_WPA_SUPPLICANT
 
 if WIFI_NM_WPA_SUPPLICANT
 
+config SYSTEM_WORKQUEUE_MIN_STACK_SIZE_WPA_SUPPLICANT
+	int
+	default 2560
+
 config HEAP_MEM_POOL_ADD_SIZE_HOSTAP
 	def_int 66560 if WIFI_NM_HOSTAPD_AP
 	def_int 48000 if WIFI_NM_WPA_SUPPLICANT_CRYPTO_ENTERPRISE

scripts/ci/check_compliance.py

@@ -1110,6 +1110,7 @@ def check_no_undef_outside_kconfig(self, kconf):
         "SRAM2",  # Referenced in a comment in samples/application_development
         "STACK_SIZE",  # Used as an example in the Kconfig docs
         "STD_CPP",  # Referenced in CMake comment
+        "SYSTEM_WORKQUEUE_MIN_STACK_SIZE_", # Used as an option matching prefix
         "TEST1",
         "TOOLCHAIN_ARCMWDT_SUPPORTS_THREAD_LOCAL_STORAGE", # The symbol is defined in the toolchain
                                                     # Kconfig which is sourced based on Zephyr

subsys/testsuite/Kconfig

@@ -72,6 +72,11 @@ config COVERAGE_GCOV
 
 endchoice
 
+config SYSTEM_WORKQUEUE_MIN_STACK_SIZE_COVERAGE_GCOV
+	int
+	depends on COVERAGE_GCOV
+	default 4096
+
 config COVERAGE_GCOV_HEAP_SIZE
 	int "Size of heap allocated for gcov coverage data dump"
 	depends on COVERAGE_GCOV