schedule: add support for user-space LL scheduler #10508

kv2019i · 2026-01-29T19:33:41Z

Series that starts building up support for running SOF LL tasks in user-space (on platforms supporting Zephyr user-space). We already have support for DP tasks, so with both LL and DP supported, in theory all audio can be moved to user-space and run in separate memory space. This will isolate audio code from direct hardware access, protect kernel memory and device driver state.

This PR contains initial support for LL scheduler and adds a separate test case to mimic usage of SOF audio pipeline, without yet bringing in any audio dependencies.

The telemetry infra is calling privileged timer functions, so if the Low-Latency tasks are run in user-space, telemetry must be disabled. Signed-off-by: Kai Vehmanen <[email protected]>

The load tracking for Low-Latency tasks depends on low-overhead access to cycle counter (e.g. CCOUNT on xtensa), which is not currently available from user-space tasks. Add a dependency to ensure the LL stats can only be enabled if LL tasks are run in kernel mode. Signed-off-by: Kai Vehmanen <[email protected]>

Add option to build SOF with support for running LL scheduler in user-space. This commit adds initial support in the scheduler and does not yet allow to run full SOF application using the new scheduler configuration, but has enough functionality to run scheduler level tests. No functional change to default build configuration where LL scheduler is run in kernel mode, or to platforms with no userspace support. Signed-off-by: Kai Vehmanen <[email protected]>

Add a test case to run tasks with low-latency (LL) scheduler in user-space. The test does not yet use any audio pipeline functionality, but uses similar interfaces towards the SOF scheduler interface. Signed-off-by: Kai Vehmanen <[email protected]>

There are multiple style variants used in SOF for CMakeLists.txt, but this file now contains multiple variants in the same file. Fix this and align style to Zephyr style (2 space for indent, no tabs, no space before opening brackets). Signed-off-by: Kai Vehmanen <[email protected]>

Copilot

Pull request overview

This PR adds initial support for running SOF Low-Latency (LL) scheduler tasks in Zephyr user-space, providing memory protection and isolation between audio code and kernel resources.

Changes:

Adds user-space LL scheduler support with dedicated memory domains and heap management
Replaces spinlocks with mutexes for user-space compatibility
Introduces test case to validate LL task creation and execution in user-space mode

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
zephyr/test/userspace/test_ll_task.c	New test case validating user-space LL scheduler functionality with task lifecycle management
zephyr/test/userspace/README.md	Documentation update describing new LL scheduler test
zephyr/test/CMakeLists.txt	Build configuration to include LL task test when CONFIG_SOF_USERSPACE_LL is enabled
zephyr/Kconfig	New CONFIG_SOF_USERSPACE_LL option for enabling user-space LL pipelines
src/schedule/zephyr_ll.c	Core LL scheduler implementation modified to support user-space execution with dynamic memory allocation
src/schedule/zephyr_domain.c	Domain thread management updated for user-space with mutex-based synchronization
src/schedule/Kconfig	Statistics logging disabled for user-space LL scheduler
src/init/init.c	Initialization hook for user-space LL resources
src/include/sof/schedule/ll_schedule_domain.h	Header updates exposing user-space LL APIs and mutex-based locking
src/include/sof/schedule/ll_schedule.h	API declarations for user-space LL heap and memory domain management
src/debug/telemetry/Kconfig	Telemetry disabled when user-space LL is enabled

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Copilot · 2026-01-29T19:35:17Z

zephyr/test/userspace/README.md

   - Test Zephyr DAI interface, together with SOF DMA
     wrapper from a user thread. Mimics the call flows done in
     sof/src/audio/dai-zephyr.c. Use cavstool.py as host runner.
+- test_ll_test.c


Corrected spelling of 'test_ll_test.c' to 'test_ll_task.c'.

Suggested change

- test_ll_test.c

- test_ll_task.c

Copilot · 2026-01-29T19:35:18Z

src/schedule/zephyr_ll.c

+	sch->lock = k_object_alloc(K_OBJ_MUTEX);
+	if (!sch->lock) {
+		tr_err(&ll_tr, "mutex allocation failed");
+		sof_heap_free(sch->heap, sch);


Using sch->heap after it should be initialized but may not be. The heap field is only set in the CONFIG_SOF_USERSPACE_LL branch, but this error path is also within that branch before heap assignment at line 611. Use the local heap variable instead.

Suggested change

sof_heap_free(sch->heap, sch);

sof_heap_free(heap, sch);

sch_heap isn't set yet

Copilot · 2026-01-29T19:35:18Z

src/schedule/zephyr_domain.c

 	ll_sch_domain_set_pdata(domain, zephyr_domain);

+	struct zephyr_domain_thread *dt = zephyr_domain->domain_thread + cpu_get_id();


Variable declaration should be at the beginning of the function or block. Move this declaration to the top of the function for consistency with C89/C90 style if required by the project, or to improve readability.

Suggested change

ll_sch_domain_set_pdata(domain, zephyr_domain);

struct zephyr_domain_thread *dt = zephyr_domain->domain_thread + cpu_get_id();

struct zephyr_domain_thread *dt;

ll_sch_domain_set_pdata(domain, zephyr_domain);

dt = zephyr_domain->domain_thread + cpu_get_id();

Copilot · 2026-01-29T19:35:18Z

src/include/sof/schedule/ll_schedule_domain.h

 #define timer_domain_init(timer, clk) zephyr_domain_init(clk)
+k_tid_t zephyr_domain_thread_tid(struct ll_schedule_domain *domain);
 #endif


Declaration of zephyr_domain_thread_tid is placed outside the CONFIG_SOF_USERSPACE_LL guard (lines 103-109) where it logically belongs based on its implementation. This function is only implemented when CONFIG_SOF_USERSPACE_LL is enabled, so its declaration should be within the same conditional block to prevent link errors.

Suggested change

#define timer_domain_init(timer, clk) zephyr_domain_init(clk)

k_tid_t zephyr_domain_thread_tid(struct ll_schedule_domain *domain);

#endif

#define timer_domain_init(timer, clk) zephyr_domain_init(clk)

#if CONFIG_SOF_USERSPACE_LL

k_tid_t zephyr_domain_thread_tid(struct ll_schedule_domain *domain);

#endif

#endif

kv2019i · 2026-01-29T19:38:12Z

Example test run (on Intel PTL):

[    0.000000] <inf> init: print_version_banner: FW ABI 0x301d001 DBG ABI 0x5003000 tags SOF:v2.14-pre-rc-386-g773835cd8fcd zephyr:v4.3.0-4334-gc1a2b3be459d src hash 0xeab6f675 (ref hash 0xeab6f675)
[    0.000000] <dbg> ll_schedule: zephyr_ll_heap_init: init ll heap 0xa0239000, size 94208 (cached)
[    0.000000] <dbg> ll_schedule: zephyr_ll_heap_init: init ll heap 0x40239000, size 94208 (uncached)
[    0.000000] <dbg> ll_schedule: zephyr_ll_scheduler_init: init on core 0

[    0.000000] <dbg> ll_schedule: zephyr_ll_scheduler_init: ll-scheduler init done, sch 0xa02391c0 sch->lock 0x400cd4f8
[    0.000000] <dbg> ll_schedule: zephyr_ll_task_init: ll-scheduler task 0xa01aaa00 init
[    0.000000] <inf> ipc: ipc_init: SOF_BOOT_TEST_STANDALONE, disabling IPC.
*** Booting Zephyr OS build v4.3.0-4334-gc1a2b3be459d ***
===================================================================
Running TESTSUITE userspace_ll
===================================================================
START - ll_task_test
[    0.000095] <dbg> ll_schedule: zephyr_ll_task_init: ll-scheduler task 0x400d5000 init
[    0.000095] <inf> sof_boot_test: ll_task_test: task init done
[    0.000095] <inf> ll_schedule: zephyr_ll_task_schedule_common: task add 0xa02392c0 0xa00ca950U priority 0 flags 0x0
[    0.000095] <dbg> ll_schedule: zephyr_domain_register: entry
[    0.000095] <dbg> ll_schedule: zephyr_domain_register: Grant access to 0x400cd4b8 (core 0, thread 0x400cd540)
[    0.000095] <dbg> ll_schedule: zephyr_domain_register: Added access to 0x40239100
[    0.000095] <inf> ll_schedule: zephyr_domain_register: zephyr_domain_register domain->type 1 domain->clk 0 domain->ticks_per_ms 38400 period 1000
[    0.000095] <dbg> ll_schedule: zephyr_domain_thread_tid: entry
[    0.000095] <dbg> ll_schedule: zephyr_domain_thread_tid: entry
[    0.000095] <dbg> ll_schedule: zephyr_domain_thread_tid: entry
[    0.000095] <dbg> ll_schedule: zephyr_ll_task_schedule_common: granting access to lock 0x400cd4f8 for thread 0x400cd540
[    0.000095] <dbg> ll_schedule: zephyr_domain_thread_tid: entry
[    0.000095] <dbg> ll_schedule: zephyr_ll_task_schedule_common: granting access to domain lock 0x40239090 for thread 0x400cd540
[    0.000095] <inf> sof_boot_test: ll_task_test: task scheduled and running
[    0.000095] <inf> ll_schedule: zephyr_domain_thread_fn: ll core 0 thread starting
[    0.000095] <dbg> ll_schedule: zephyr_ll_run: entry
[    0.000095] <inf> sof_boot_test: task_callback: entry
[    0.000095] <dbg> ll_schedule: zephyr_ll_run: entry
[    0.000095] <inf> sof_boot_test: task_callback: entry
[    0.000095] <dbg> ll_schedule: zephyr_ll_run: entry
[    0.000095] <inf> sof_boot_test: task_callback: entry
[    0.000096] <dbg> ll_schedule: zephyr_ll_run: entry
[    0.000096] <inf> sof_boot_test: task_callback: entry
[    0.000096] <inf> ll_schedule: zephyr_ll_task_done: task complete 0xa02392c0 0xa00ca950U
[    0.000096] <inf> ll_schedule: zephyr_ll_task_done: num_tasks 1 total_num_tasks 1
[    0.000096] <dbg> ll_schedule: zephyr_domain_unregister: entry
[    0.000096] <inf> ll_schedule: zephyr_domain_unregister: zephyr_domain_unregister domain->type 1 domain->clk 0
[    0.000096] <dbg> ll_schedule: zephyr_domain_unregister: exit
[    0.000098] <inf> sof_boot_test: ll_task_test: test complete
 PASS - ll_task_test in 0.011 seconds

lyakh · 2026-01-30T08:25:02Z

src/include/sof/schedule/ll_schedule.h

 #define schedule_task_init_ll zephyr_ll_task_init

+struct task *zephyr_ll_task_alloc(void);
+k_tid_t zephyr_ll_get_thread(int core);


nitpick: I think we use struct k_thread * mostly in SOF and it seems to "work better" with various simulation / testing builds, I was getting "undefined" errors when I tried to use k_tid_t

lyakh · 2026-01-30T08:26:26Z

src/include/sof/schedule/ll_schedule_domain.h


+#if defined(__ZEPHYR__)
+struct ll_schedule_domain *zephyr_ll_domain(void);
+struct ll_schedule_domain *zephyr_domain_init(int clk);


zephyr_ll_domain_init()?

lyakh · 2026-01-30T08:35:26Z

src/include/sof/schedule/ll_schedule_domain.h

+	struct k_mutex *lock;		/**< standard lock */
+#else
+	struct k_spinlock lock;         /**< standard lock */
+#endif


note: this change actually modifies the current behaviour already.

Ack @lyakh , discussed offline and I think I'll go back a step and keep the kernel LL build using spinlocks (and/or make it a separate PR).

lyakh · 2026-01-30T08:40:36Z

src/include/sof/schedule/ll_schedule_domain.h

+
+#if defined(CONFIG_SOF_USERSPACE_LL)
+	/* Allocate mutex dynamically for userspace access */
+	domain->lock = k_object_alloc(K_OBJ_MUTEX);


I think this allocates cached?

lyakh · 2026-01-30T08:47:39Z

src/schedule/zephyr_domain.c


+#if CONFIG_SOF_USERSPACE_LL
+
+k_tid_t zephyr_domain_thread_tid(struct ll_schedule_domain *domain)


struct k_thread * maybe

lyakh · 2026-01-30T09:33:40Z

src/schedule/zephyr_ll.c

+
 	list_init(&sch->tasks);
 	sch->ll_domain = domain;
 	sch->core = cpu_get_id();


lyakh · 2026-01-30T09:34:58Z

src/schedule/zephyr_ll.c

+	sch->lock = k_object_alloc(K_OBJ_MUTEX);
+	if (!sch->lock) {
+		tr_err(&ll_tr, "mutex allocation failed");
+		sof_heap_free(sch->heap, sch);


sch_heap isn't set yet

lyakh · 2026-01-30T09:45:19Z

zephyr/test/userspace/test_ll_task.c

+ZTEST(userspace_ll, ll_task_test)
+{
+	ll_task_test();
+	ztest_test_pass();


I actually removed these from my tests, they're doing some long jumps... Are you sure you need this?

lyakh · 2026-01-30T09:46:13Z

zephyr/test/userspace/test_ll_task.c

+ * SOF main has booted up and IPC handling is stopped.
+ * Run test suites with ztest_run_all.
+ */
+static int run_tests(void)


would be good to have a similar test for DP

lyakh · 2026-01-30T09:50:13Z

zephyr/test/CMakeLists.txt


-if (CONFIG_SOF_BOOT_TEST_STANDALONE AND CONFIG_SOF_USERSPACE_LL)
+if(CONFIG_SOF_BOOT_TEST_STANDALONE AND CONFIG_SOF_USERSPACE_LL)
  zephyr_library_sources(userspace/test_ll_task.c)


looks like aligning to use TABs instead would make the path smaller

softwarecki

First quick remarks. I still have 2 commits left to review... There is a lot of conditional code added here. Would it not be better to make this a separate scheduler? SOF already supports multiple different schedulers

softwarecki · 2026-01-30T12:52:15Z

src/include/sof/schedule/ll_schedule_domain.h


+#if defined(__ZEPHYR__) && CONFIG_SOF_USERSPACE_LL
+	domain = sof_heap_alloc(zephyr_ll_heap(), SOF_MEM_FLAG_USER | SOF_MEM_FLAG_COHERENT,
+				sizeof(*domain), sizeof(void *));


Missing memset

softwarecki · 2026-01-30T12:56:24Z

src/include/sof/schedule/ll_schedule_domain.h

+	domain->lock = rzalloc(SOF_MEM_FLAG_KERNEL | SOF_MEM_FLAG_COHERENT, sizeof(*domain->lock));
+#endif
+	if (!domain->lock) {
+		rfree(domain);


heap_free(zephyr_ll_heap(), ... for CONFIG_SOF_USERSPACE_LL?

softwarecki · 2026-01-30T13:09:33Z

src/schedule/zephyr_domain.c

+#endif /* CONFIG_SOF_USERSPACE_LL */
+
 struct zephyr_domain_thread {
-	struct k_thread ll_thread;


Can we keep these static objects when CONFIG_SOF_USERSPACE_LL is not enabled? We could keep pointer fields that point to static objects, similar to the dp scheduler solution.

softwarecki · 2026-01-30T13:58:38Z

src/schedule/zephyr_domain.c

+	}

-	key = k_spin_lock(&domain->lock);
+	k_mutex_lock(domain->lock, K_FOREVER);


spinlock still in use without defined(__ZEPHYR__)

softwarecki · 2026-01-30T14:02:06Z

src/schedule/zephyr_domain.c

+	       (void *)mem_partition.start,
+	       heap->heap.init_bytes);
+
+	mem_partition.start = (uintptr_t)sys_cache_uncached_ptr_get(heap->heap.init_mem);


Zephyr maps cached and non-cached addresses when the double map config is enabled. Maybe it is worth check it here?

softwarecki · 2026-01-30T14:03:25Z

src/schedule/zephyr_domain.c

+void zephyr_ll_resources_init(void)
+{
+	k_mem_domain_init(&ll_mem_resources.mem_domain, 0, NULL);
+	k_mutex_init(&ll_mem_resources.lock);


Static kobjects are initialized by default, so there is no need to initialize them manually.

softwarecki · 2026-01-30T14:06:09Z

src/schedule/zephyr_domain.c

+	zephyr_domain->timer = k_object_alloc(K_OBJ_TIMER);
+	if (!zephyr_domain->timer) {
+		tr_err(&ll_tr, "timer allocation failed");
+		rfree(zephyr_domain);


heap_free(zephyr_ll_heap(), ...

softwarecki · 2026-01-30T14:09:25Z

src/schedule/zephyr_domain.c

+	/* Add zephyr_domain_ops to the memory domain for user thread access */
+	struct k_mem_partition ops_partition;
+
+	ops_partition.start = (uintptr_t)&zephyr_domain_ops;


Partition size must be aligned to page size. Consider use APP_TASK_DATA in the zephyr_domain_ops declatarion.

kv2019i added 5 commits January 29, 2026 20:50

debug: telemetry: add a dependency to kernel mode LL thread

151f8af

The telemetry infra is calling privileged timer functions, so if the Low-Latency tasks are run in user-space, telemetry must be disabled. Signed-off-by: Kai Vehmanen <[email protected]>

Copilot AI review requested due to automatic review settings January 29, 2026 19:33

kv2019i requested review from LaurentiuM1234, abonislawski, dbaluta, iuliana-prodan, lbetlej, lgirdwood, lyakh, marcinszkudlinski, mmaka1, pblaszko and plbossart as code owners January 29, 2026 19:33

kv2019i requested review from jsarha and softwarecki January 29, 2026 19:34

Copilot AI reviewed Jan 29, 2026

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lyakh reviewed Jan 30, 2026

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softwarecki reviewed Jan 30, 2026

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		ll_sch_domain_set_pdata(domain, zephyr_domain);

		struct zephyr_domain_thread *dt = zephyr_domain->domain_thread + cpu_get_id();


		#if CONFIG_SOF_USERSPACE_LL

		k_tid_t zephyr_domain_thread_tid(struct ll_schedule_domain *domain)

schedule: add support for user-space LL scheduler #10508

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schedule: add support for user-space LL scheduler #10508

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