kernel/git/stable/linux-stable.git/tools/sched_ext, branch master

sched_ext: Maintain an online cid mask in the scheduler arena

2026-09-15T16:57:20+00:00

Schedulers on the default cid mapping treat [0, nr_online_cids) as the online set and restart on hotplug. Schedulers that install their own mapping with scx_bpf_cid_override() have no way to learn which cids are online: the count no longer identifies members and the CPU-form cpumask is unusable from cid programs. This is an obvious hole in the cid API. Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's arena, allocated alongside the per-CPU scratch masks and populated after the cid mapping is finalized and before ops.init(), for child schedulers too. The pointer stays valid through ops.exit() with no reference to take. It is the arena offset as a void pointer, the same form struct_ops arena arguments arrive in. The verifier types the void return as a scalar for the program's arena cast. The mask follows the SCX hotplug notifications: seeded from cpu_active_mask and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask only inside a hotplug transition. Updates walk the scheduler list under the lock that also serializes unlinking. Reads are live, not atomic snapshots. Root initialization excludes hotplug. v2: Reworded the getter kerneldoc (Andrea Righi). Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi

sched_ext: scx_qmap: Restore unused idle claims from ops.dispatch()

2026-09-15T16:57:19+00:00

scx_qmap tracks idle cids itself. pick_direct_dispatch_cid() claims a cid by clearing its bit and the task is inserted into that cid's local DSQ, which kicks the CPU. When the task does not arrive, for example because the insert fell back to the global DSQ after an affinity change, the CPU wakes, finds nothing and picks idle again. That is not an idle transition, so ops.update_idle() is not called and the cid stays marked busy until an unrelated task runs on it. Restore the claim from ops.dispatch(). The kick guarantees a dispatch on the kicked CPU, and when it finds nothing to run with a NULL @prev, the CPU is going back to idle. Document the pattern in ops.update_idle(), which reports only actual transitions. Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi Cc: Andrea Righi

sched_ext: scx_qmap: Fix pending partition work handoff

2026-09-06T22:39:15+00:00

qmap can leave partition work pending with no runner. The effective-cap callback publishes its request after failing to acquire part_busy, while redistribute() checks for pending work before releasing it. Either ordering can miss a request arriving as the current runner finishes, delaying the update until the round-robin timer runs. Publish requests before trying to become the runner and release part_busy before checking for more work. Have all holders drain pending requests after releasing it, including the stats flush. Distinguish mask refreshes from repartitions so an effective-cap update only rebuilds the partition when a repartition was also requested. Fixes: e9151ed5c944 ("tools/sched_ext: scx_qmap - Expand hierarchical sub-scheduling") Reported-by: Andrea Righi Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi

sched_ext: scx_qmap: Place only on cids whose caps are in effect

2026-09-05T22:12:28+00:00

qmap decides placements from self_cids, which redistribute() derives from the caps view at ops.sub_caps_updated() time. That view runs ahead of the cpus: a granted cid can be in self_cids before its cpu has reported the caps in effect through ops.sub_ecaps_updated(). ops.update_idle() only comes once BASE is in effect, so the idle-gated placements reach such a cid only through an idle bit left over from an earlier hold. The highpri scan has no gate at all: parent cpu Y, qmap cpu X grants ENQ on X to qmap sub_caps_updated() adds X to self_cids highpri scan moves a task to X with PREEMPT caps not in effect, move denied, task bounced with REENQ_CAP reject drain, enqueue the scan moves it to X again denied again dispatch syncs ecaps, sub_ecaps_updated(X) Every highpri move to X in that window is denied and bounced. The two callbacks are meant to split the roles: ops.sub_caps_updated() tracks what the node holds and drives what it delegates to its children, while ops.sub_ecaps_updated() says whether a task can run on a cpu now. qmap used the first for both. Track the caps in effect from ops.sub_ecaps_updated() as avail_cids and place only on self_cids & avail_cids, so that self_cids stays the delegation split and avail_cids gates the placement. The stranded tests keep self_cids, as they ask whether the split gives the task anywhere at all. A highpri task whose self_cids lack caps in effect waits for them instead of being moved and bounced. Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi

sched_ext: scx_qmap: Do not add IMMED to rescue inserts

2026-09-05T22:12:20+00:00

qmap's stranded fallback forces a task that can run on none of its self cids onto its first allowed cid with SCX_ENQ_RESCUE, and adds SCX_ENQ_IMMED when that cid is a time-share it holds. On such a cid the insert stops being a rescue request: 1. A task is enqueued while none of its allowed cids is in self_cids. At attach self_cids is still empty. 2. qmap inserts it into cid 0's local DSQ with SCX_ENQ_RESCUE | SCX_ENQ_IMMED. 3. The kernel finds ENQ_IMMED held on cid 0, admits the insert and skips the rescue diversion. 4. cid 0's cpu is busy, so the IMMED task is bounced back to qmap with SCX_ENQ_REENQ. 5. qmap's enqueue sees the same inputs and repeats step 2. Nothing runs in between. 6. The reenqueue limit ejects qmap with SCX_EXIT_ERROR_REENQ. The caps granted during the parent's ops.sub_attach() are delivered after the sub already holds its tasks, while the per-cid effective caps that mark the time-shares are delivered from the first dispatch after bypass lifts, so every attach that receives a time-share on a task's first allowed cid starts the loop. Drop IMMED from the rescue inserts so that step 3 diverts to the rescue path. Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi

sched_ext: Check bpf_timer_start return values in scx_qmap

2026-08-31T16:47:39+00:00

monitor_timerfn(), lowpri_timerfn() and round_robin_timerfn() ignore bpf_timer_start()'s return value: a failed re-arm silently stops the periodic heartbeat, starving every task parked in LOWPRI_DSQ (lowpri) or freezing cid rotation (round-robin). Check the returns and raise scx_bpf_error(), matching the init paths. Signed-off-by: Wanwu Li Signed-off-by: Tejun Heo

sched_ext: Fix vtime delta loss in scx_flatcg cgroup migration

2026-08-31T16:47:33+00:00

fcg_cgroup_move() lost the signed vtime offset across cgroup migration in the mechanical conversion to time helpers: time_delta() clamps negative deltas to 0, so a queued task (whose dsq_vtime is normally behind the source frontier) loses its accumulated vtime credit and lands exactly at the destination frontier instead of keeping its relative position. Restore the wrapping signed subtraction. Fixes: 62addc6dbf36 ("sched_ext: Use time helpers in BPF schedulers") Signed-off-by: Wanwu Li Signed-off-by: Tejun Heo

sched_ext: Fix timer pinning and return value in scx_central

2026-08-31T16:47:26+00:00

central_timerfn() re-arms the timer with a hardcoded BPF_F_TIMER_CPU_PIN flag and ignores the return value, defeating start_central_timer()'s -EINVAL fallback for kernels without the flag (<6.7): on such kernels the first tick kills the timer permanently with no diagnostic. Honor timer_pinned and check the return like the initial arm does. Fixes: 22a920209ab6 ("sched_ext: Implement tickless support") Signed-off-by: Wanwu Li Signed-off-by: Tejun Heo

sched_ext: Sync common and compat headers from the scx repo

2026-08-22T07:19:26+00:00

Sync common.bpf.h, compat.bpf.h and compat.h with the scx repo, which accumulated the following: - __COMPAT_read_enum() can now recover 64-bit scx enum values from kernel BTF generated without BTF_KIND_ENUM64 support (pahole < 1.24 or --skip_encoding_btf_enum64, e.g. COS/GKE kernels), substituting values from the build-time vmlinux.h cross-checked against the low 32 bits the kernel does provide. - is_migration_disabled() no longer assumes the BPF prolog always disables migration. Since 8e4f0b1ebcf2 ("bpf: use rcu_read_lock_dont_migrate() for trampoline.c") the prolog only does so under CONFIG_PREEMPT_RCU, so the old current-task test under-reported on v6.18+ !PREEMPT_RCU kernels. A runtime probe on bpf_scx_reg() handles older kernels with backported trampoline behavior. - __COMPAT_scx_bpf_dsq_peek() is gated behind kernel v7.1 where 2f2ea7709266 ("sched_ext: Use dsq->first_task instead of list_empty() in dispatch_enqueue() FIFO-tail") fixed the kfunc spuriously returning NULL on non-empty FIFO DSQs, and the new scx_bpf_reenqueue_local_from_anywhere() provides a callable-from-anywhere reenqueue which prefers the generic scx_bpf_dsq_reenq(). Both were first posted by Gavin Guo and Changwoo Min and are picked up here with the review feedback folded in. - __COMPAT_scx_bpf_cpu_curr() and the scx_bpf_cpu_rq() declaration are restored. Schedulers built from these headers still run on pre-v6.18 kernels where scx_bpf_cpu_curr() does not resolve and the scx_bpf_cpu_rq() fallback still exists. - scx_clock_task() and scx_clock_pelt() document their stale-read behavior for remote idle CPUs under NO_HZ_IDLE. Link: https://lore.kernel.org/all/20260817143126.562923-1-changwoo@igalia.com Signed-off-by: Tejun Heo

sched_ext: Sync tools autogen enum headers from the scx repo

2026-08-22T07:19:26+00:00

Regenerate enum_defs.autogen.h against the current tree, picking up the dispatch verdict enums and dropping the marker for the removed SCX_RQ_IN_BALANCE. Add enums_abi.autogen.h, a table of 64-bit scx enumerator values generated from vmlinux.h, used as the substitution source when the running kernel's BTF truncates 64-bit enum values to 32 bits. Signed-off-by: Tejun Heo