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Tue, 27 Jan 2026 08:53:58 -0800 (PST) Precedence: bulk X-Mailing-List: sched-ext@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 27 Jan 2026 11:53:57 -0500 Message-Id: From: "Emil Tsalapatis" To: "Andrea Righi" , "Tejun Heo" , "David Vernet" , "Changwoo Min" Cc: "Kuba Piecuch" , "Christian Loehle" , "Daniel Hodges" , , Subject: Re: [PATCH 2/2] selftests/sched_ext: Add test to validate ops.dequeue() semantics X-Mailer: aerc 0.20.1 References: <20260126084258.3798129-1-arighi@nvidia.com> <20260126084258.3798129-3-arighi@nvidia.com> In-Reply-To: <20260126084258.3798129-3-arighi@nvidia.com> On Mon Jan 26, 2026 at 3:41 AM EST, Andrea Righi wrote: > Add a new kselftest to validate that: > - every enqueue is followed by proper dequeue, > - dispatch dequeues happen exactly once per enqueue, > - property change dequeues (%SCX_DEQ_SCHED_CHANGE) only happen for > property changes, > - no duplicate enqueues without proper dequeue. > > Test scenarios: > - direct dispatch to local DSQ (%SCX_DSQ_LOCAL), > - dispatch to user DSQ, > - explicit property changes via sched_setaffinity(). > > This validates that the new ops.dequeue() semantics work correctly for > all task lifecycle scenarios. > > Cc: Tejun Heo > Cc: Emil Tsalapatis > Cc: Kuba Piecuch > Signed-off-by: Andrea Righi Reviewed-by: Emil Tsalapatis > --- > tools/testing/selftests/sched_ext/Makefile | 1 + > .../testing/selftests/sched_ext/dequeue.bpf.c | 209 ++++++++++++++++++ > tools/testing/selftests/sched_ext/dequeue.c | 182 +++++++++++++++ > 3 files changed, 392 insertions(+) > create mode 100644 tools/testing/selftests/sched_ext/dequeue.bpf.c > create mode 100644 tools/testing/selftests/sched_ext/dequeue.c > > diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/s= elftests/sched_ext/Makefile > index 5fe45f9c5f8fd..764e91edabf93 100644 > --- a/tools/testing/selftests/sched_ext/Makefile > +++ b/tools/testing/selftests/sched_ext/Makefile > @@ -161,6 +161,7 @@ all_test_bpfprogs :=3D $(foreach prog,$(wildcard *.bp= f.c),$(INCLUDE_DIR)/$(patsubs > =20 > auto-test-targets :=3D \ > create_dsq \ > + dequeue \ > enq_last_no_enq_fails \ > ddsp_bogus_dsq_fail \ > ddsp_vtimelocal_fail \ > diff --git a/tools/testing/selftests/sched_ext/dequeue.bpf.c b/tools/test= ing/selftests/sched_ext/dequeue.bpf.c > new file mode 100644 > index 0000000000000..8b2f792cf7d8b > --- /dev/null > +++ b/tools/testing/selftests/sched_ext/dequeue.bpf.c > @@ -0,0 +1,209 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * A scheduler that validates ops.dequeue() is called correctly: > + * - For tasks on BPF data structures (not yet dispatched) > + * - For tasks already on DSQs (local or shared) > + * - That every ops.enqueue() is followed by ops.dequeue() > + * > + * Copyright (c) 2025 NVIDIA Corporation. > + */ > + > +#include > + > +#define SHARED_DSQ 0 > + > +char _license[] SEC("license") =3D "GPL"; > + > +UEI_DEFINE(uei); > + > +/* > + * Counters to track the lifecycle of tasks: > + * - enqueue_cnt: Number of times ops.enqueue() was called > + * - dequeue_cnt: Number of times ops.dequeue() was called (any type) > + * - dispatch_dequeue_cnt: Number of regular dispatch dequeues (no flag) > + * - change_dequeue_cnt: Number of property change dequeues (%SCX_DEQ_SC= HED_CHANGE) > + */ > +u64 enqueue_cnt, dequeue_cnt, dispatch_dequeue_cnt, change_dequeue_cnt; > + > +/* > + * Test scenarios: > + * - 0: Dispatch to local DSQ > + * - 1: Dispatch to shared DSQ > + */ > +u32 test_scenario; > + > +/* > + * Per-task state to track lifecycle and validate workflow semantics. > + * State transitions: > + * NONE -> ENQUEUED (on enqueue) > + * ENQUEUED -> DISPATCHED (on dispatch dequeue) > + * DISPATCHED -> NONE (on property change dequeue or re-enqueue) > + * ENQUEUED -> NONE (on property change dequeue before dispatch) > + */ > +enum task_state { > + TASK_NONE =3D 0, /* Task is outside scheduler control */ > + TASK_ENQUEUED, /* ops.enqueue() called, waiting for dequeue */ > + TASK_DISPATCHED, /* Dispatch dequeue received, can get property chan= ge or re-enqueue */ > +}; > + > +struct task_ctx { > + enum task_state state; /* Current state in the workflow */ > + u64 enqueue_seq; /* Sequence number for debugging */ > +}; > + > +struct { > + __uint(type, BPF_MAP_TYPE_TASK_STORAGE); > + __uint(map_flags, BPF_F_NO_PREALLOC); > + __type(key, int); > + __type(value, struct task_ctx); > +} task_ctx_stor SEC(".maps"); > + > +static struct task_ctx *try_lookup_task_ctx(struct task_struct *p) > +{ > + return bpf_task_storage_get(&task_ctx_stor, p, 0, 0); > +} > + > +s32 BPF_STRUCT_OPS(dequeue_select_cpu, struct task_struct *p, > + s32 prev_cpu, u64 wake_flags) > +{ > + /* Always bounce to ops.enqueue() */ > + return prev_cpu; > +} > + > +void BPF_STRUCT_OPS(dequeue_enqueue, struct task_struct *p, u64 enq_flag= s) > +{ > + struct task_ctx *tctx; > + > + __sync_fetch_and_add(&enqueue_cnt, 1); > + > + tctx =3D try_lookup_task_ctx(p); > + if (!tctx) > + return; > + > + /* > + * Validate state transition: enqueue is only valid from NONE or > + * DISPATCHED states. Getting enqueue while in ENQUEUED state > + * indicates a missing dequeue. > + */ > + if (tctx->state =3D=3D TASK_ENQUEUED) > + scx_bpf_error("%d (%s): enqueue while in ENQUEUED state (seq %llu)", > + p->pid, p->comm, tctx->enqueue_seq); > + > + /* Transition to ENQUEUED state */ > + tctx->state =3D TASK_ENQUEUED; > + tctx->enqueue_seq++; > + > + switch (test_scenario) { > + case 0: > + /* Scenario 0: Direct dispatch to the local DSQ */ > + scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, enq_flags); > + break; > + > + case 1: > + /* Scenario 1: Dispatch to shared DSQ */ > + scx_bpf_dsq_insert(p, SHARED_DSQ, SCX_SLICE_DFL, enq_flags); > + break; > + } > +} > + > +void BPF_STRUCT_OPS(dequeue_dequeue, struct task_struct *p, u64 deq_flag= s) > +{ > + struct task_ctx *tctx; > + > + __sync_fetch_and_add(&dequeue_cnt, 1); > + > + tctx =3D try_lookup_task_ctx(p); > + if (!tctx) > + return; > + > + /* > + * Validate state: dequeue should only happen from ENQUEUED or > + * DISPATCHED states. Getting dequeue from NONE indicates a bug. > + */ > + if (tctx->state =3D=3D TASK_NONE) > + scx_bpf_error("%d (%s): dequeue from NONE state (seq %llu)", > + p->pid, p->comm, tctx->enqueue_seq); > + > + if (deq_flags & SCX_DEQ_SCHED_CHANGE) { > + /* > + * Async dequeue: property change interrupting the workflow. > + * Valid from both ENQUEUED and DISPATCHED states. > + * Transitions task back to NONE state. > + */ > + __sync_fetch_and_add(&change_dequeue_cnt, 1); > + > + /* Validate state transition */ > + if (tctx->state !=3D TASK_ENQUEUED && tctx->state !=3D TASK_DISPATCHED= ) > + scx_bpf_error("%d (%s): property change dequeue from invalid state %d= (seq %llu)", > + p->pid, p->comm, tctx->state, tctx->enqueue_seq); > + > + /* Transition back to NONE - task outside scheduler control */ > + tctx->state =3D TASK_NONE; > + } else { > + /* > + * Regular dispatch dequeue: normal workflow step. > + * Valid only from ENQUEUED state (after enqueue, before dispatch dequ= eue). > + * Transitions to DISPATCHED state. > + */ > + __sync_fetch_and_add(&dispatch_dequeue_cnt, 1); > + > + /* Validate: dispatch dequeue should NOT have %SCX_DEQ_SCHED_CHANGE fl= ag */ > + if (deq_flags & SCX_DEQ_SCHED_CHANGE) > + scx_bpf_error("%d (%s): SCX_DEQ_SCHED_CHANGE in dispatch dequeue (seq= %llu)", > + p->pid, p->comm, tctx->enqueue_seq); > + > + /* Must be in ENQUEUED state */ > + if (tctx->state !=3D TASK_ENQUEUED) > + scx_bpf_error("%d (%s): dispatch dequeue from state %d (seq %llu)", > + p->pid, p->comm, tctx->state, tctx->enqueue_seq); > + > + /* Transition to DISPATCHED - normal cycle completed dispatch */ > + tctx->state =3D TASK_DISPATCHED; > + } > +} > + > +void BPF_STRUCT_OPS(dequeue_dispatch, s32 cpu, struct task_struct *prev) > +{ > + scx_bpf_dsq_move_to_local(SHARED_DSQ); > +} > + > +s32 BPF_STRUCT_OPS(dequeue_init_task, struct task_struct *p, > + struct scx_init_task_args *args) > +{ > + struct task_ctx *tctx; > + > + tctx =3D bpf_task_storage_get(&task_ctx_stor, p, 0, > + BPF_LOCAL_STORAGE_GET_F_CREATE); > + if (!tctx) > + return -ENOMEM; > + > + return 0; > +} > + > +s32 BPF_STRUCT_OPS_SLEEPABLE(dequeue_init) > +{ > + s32 ret; > + > + ret =3D scx_bpf_create_dsq(SHARED_DSQ, -1); > + if (ret) > + return ret; > + > + return 0; > +} > + > +void BPF_STRUCT_OPS(dequeue_exit, struct scx_exit_info *ei) > +{ > + UEI_RECORD(uei, ei); > +} > + > +SEC(".struct_ops.link") > +struct sched_ext_ops dequeue_ops =3D { > + .select_cpu =3D (void *)dequeue_select_cpu, > + .enqueue =3D (void *)dequeue_enqueue, > + .dequeue =3D (void *)dequeue_dequeue, > + .dispatch =3D (void *)dequeue_dispatch, > + .init_task =3D (void *)dequeue_init_task, > + .init =3D (void *)dequeue_init, > + .exit =3D (void *)dequeue_exit, > + .name =3D "dequeue_test", > +}; > diff --git a/tools/testing/selftests/sched_ext/dequeue.c b/tools/testing/= selftests/sched_ext/dequeue.c > new file mode 100644 > index 0000000000000..6861257d79b47 > --- /dev/null > +++ b/tools/testing/selftests/sched_ext/dequeue.c > @@ -0,0 +1,182 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Copyright (c) 2025 NVIDIA Corporation. > + */ > +#define _GNU_SOURCE > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include "scx_test.h" > +#include "dequeue.bpf.skel.h" > + > +#define NUM_WORKERS 8 > + > +/* > + * Worker function that creates enqueue/dequeue events. It alternates > + * between CPU work, sleeping, and affinity changes to trigger dequeues. > + */ > +static void worker_fn(int id) > +{ > + cpu_set_t cpuset; > + int i; > + volatile int sum =3D 0; > + > + for (i =3D 0; i < 1000; i++) { > + int j; > + > + /* Do some work to trigger scheduling events */ > + for (j =3D 0; j < 10000; j++) > + sum +=3D j; > + > + /* Change affinity to trigger dequeue */ > + if (i % 10 =3D=3D 0) { > + CPU_ZERO(&cpuset); > + /* Rotate through the first 4 CPUs */ > + CPU_SET(i % 4, &cpuset); > + sched_setaffinity(0, sizeof(cpuset), &cpuset); > + } > + > + /* Do additional work */ > + for (j =3D 0; j < 10000; j++) > + sum +=3D j; > + > + /* Sleep to trigger dequeue */ > + usleep(1000 + (id * 100)); > + } > + > + exit(0); > +} > + > +static enum scx_test_status run_scenario(struct dequeue *skel, u32 scena= rio, > + const char *scenario_name) > +{ > + struct bpf_link *link; > + pid_t pids[NUM_WORKERS]; > + int i, status; > + u64 enq_start, deq_start, dispatch_deq_start, change_deq_start; > + u64 enq_delta, deq_delta, dispatch_deq_delta, change_deq_delta; > + > + /* Set the test scenario */ > + skel->bss->test_scenario =3D scenario; > + > + /* Record starting counts */ > + enq_start =3D skel->bss->enqueue_cnt; > + deq_start =3D skel->bss->dequeue_cnt; > + dispatch_deq_start =3D skel->bss->dispatch_dequeue_cnt; > + change_deq_start =3D skel->bss->change_dequeue_cnt; > + > + link =3D bpf_map__attach_struct_ops(skel->maps.dequeue_ops); > + SCX_FAIL_IF(!link, "Failed to attach struct_ops for scenario %s", scena= rio_name); > + > + /* Fork worker processes to generate enqueue/dequeue events */ > + for (i =3D 0; i < NUM_WORKERS; i++) { > + pids[i] =3D fork(); > + SCX_FAIL_IF(pids[i] < 0, "Failed to fork worker %d", i); > + > + if (pids[i] =3D=3D 0) { > + worker_fn(i); > + /* Should not reach here */ > + exit(1); > + } > + } > + > + /* Wait for all workers to complete */ > + for (i =3D 0; i < NUM_WORKERS; i++) { > + SCX_FAIL_IF(waitpid(pids[i], &status, 0) !=3D pids[i], > + "Failed to wait for worker %d", i); > + SCX_FAIL_IF(status !=3D 0, "Worker %d exited with status %d", i, statu= s); > + } > + > + bpf_link__destroy(link); > + > + SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_UNREG)); > + > + /* Calculate deltas */ > + enq_delta =3D skel->bss->enqueue_cnt - enq_start; > + deq_delta =3D skel->bss->dequeue_cnt - deq_start; > + dispatch_deq_delta =3D skel->bss->dispatch_dequeue_cnt - dispatch_deq_s= tart; > + change_deq_delta =3D skel->bss->change_dequeue_cnt - change_deq_start; > + > + printf("%s:\n", scenario_name); > + printf(" enqueues: %lu\n", (unsigned long)enq_delta); > + printf(" dequeues: %lu (dispatch: %lu, property_change: %lu)\n", > + (unsigned long)deq_delta, > + (unsigned long)dispatch_deq_delta, > + (unsigned long)change_deq_delta); > + > + /* > + * Validate that we got enqueue and dequeue events. > + * The BPF code does strict state machine validation with scx_bpf_error= () > + * to ensure the workflow semantics are correct. If we reach here witho= ut > + * errors, the semantics are validated correctly. > + */ > + SCX_GT(enq_delta, 0); > + SCX_GT(deq_delta, 0); > + > + return SCX_TEST_PASS; > +} > + > +static enum scx_test_status setup(void **ctx) > +{ > + struct dequeue *skel; > + > + skel =3D dequeue__open(); > + SCX_FAIL_IF(!skel, "Failed to open skel"); > + SCX_ENUM_INIT(skel); > + SCX_FAIL_IF(dequeue__load(skel), "Failed to load skel"); > + > + *ctx =3D skel; > + > + return SCX_TEST_PASS; > +} > + > +static enum scx_test_status run(void *ctx) > +{ > + struct dequeue *skel =3D ctx; > + enum scx_test_status status; > + > + status =3D run_scenario(skel, 0, "Local DSQ"); > + if (status !=3D SCX_TEST_PASS) > + return status; > + > + status =3D run_scenario(skel, 1, "User DSQ"); > + if (status !=3D SCX_TEST_PASS) > + return status; > + > + printf("\n=3D=3D=3D Summary =3D=3D=3D\n"); > + printf("Total enqueues: %lu\n", (unsigned long)skel->bss->enqueue_cnt); > + printf("Total dequeues: %lu\n", (unsigned long)skel->bss->dequeue_cnt); > + printf(" Dispatch dequeues: %lu (no flag, normal workflow)\n", > + (unsigned long)skel->bss->dispatch_dequeue_cnt); > + printf(" Property change dequeues: %lu (SCX_DEQ_SCHED_CHANGE flag)\n", > + (unsigned long)skel->bss->change_dequeue_cnt); > + printf("\nAll scenarios passed - no state machine violations detected\n= "); > + printf("-> Validated: Correct state transitions (NONE -> ENQUEUED -> DI= SPATCHED)\n"); > + printf("-> Validated: Dispatch dequeues have no flags (normal workflow)= \n"); > + printf("-> Validated: Async dequeues have SCX_DEQ_SCHED_CHANGE flag (in= terruptions)\n"); > + printf("-> Validated: No duplicate enqueues or invalid state transition= s\n"); > + > + return SCX_TEST_PASS; > +} > + > +static void cleanup(void *ctx) > +{ > + struct dequeue *skel =3D ctx; > + > + dequeue__destroy(skel); > +} > + > +struct scx_test dequeue_test =3D { > + .name =3D "dequeue", > + .description =3D "Verify that ops.enqueue() is balanced with ops.dequeu= e()", > + .setup =3D setup, > + .run =3D run, > + .cleanup =3D cleanup, > +}; > + > +REGISTER_SCX_TEST(&dequeue_test)