Merge tag 'sched_ext-for-7.0-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext

Pull sched_ext fixes from Tejun Heo:

- Various bug fixes for the example schedulers and selftests

Merge tag 'sched_ext-for-7.0-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext

Pull sched_ext fixes from Tejun Heo:

- Various bug fixes for the example schedulers and selftests

* tag 'sched_ext-for-7.0-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
tools/sched_ext: fix getopt not re-parsed on restart
tools/sched_ext: scx_userland: fix data races on shared counters
tools/sched_ext: scx_pair: fix stride == 0 crash on single-CPU systems
tools/sched_ext: scx_central: fix CPU_SET and skeleton leak on early exit
tools/sched_ext: scx_userland: fix stale data on restart
tools/sched_ext: scx_flatcg: fix potential stack overflow from VLA in fcg_read_stats
selftests/sched_ext: Fix rt_stall flaky failure
tools/sched_ext: scx_userland: fix restart and stats thread lifecycle bugs
tools/sched_ext: scx_central: fix sched_setaffinity() call with the set size
tools/sched_ext: scx_flatcg: zero-initialize stats counter array

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selftests/sched_ext: Fix rt_stall flaky failure

The rt_stall test measures the runtime ratio between an EXT and an RT
task pinned to the same CPU, verifying that the deadline server prevents
RT task

selftests/sched_ext: Fix rt_stall flaky failure

The rt_stall test measures the runtime ratio between an EXT and an RT
task pinned to the same CPU, verifying that the deadline server prevents
RT tasks from starving SCHED_EXT tasks. It expects the EXT task to get
at least 4% of CPU time.

The test is flaky because sched_stress_test() calls sleep(RUN_TIME)
immediately after fork(), without waiting for the RT child to complete
its setup (set_affinity + set_sched). If the RT child experiences
scheduling latency before completing setup, that delay eats into the
measurement window: the RT child runs for less than RUN_TIME seconds,
and the EXT task's measured ratio drops below the 4% threshold.

For example, in the failing CI run [1]:
EXT=0.140s RT=4.750s total=4.890s (expected ~5.0s)
ratio=2.86% < 4% → FAIL

The 110ms gap (5.0 - 4.89) corresponds to the RT child's setup time
being counted inside the measurement window, during which fewer
deadline server ticks fire for the EXT task.

Fix by using pipes to synchronize: each child signals the parent after
completing its setup, and the parent waits for both signals before
starting sleep(RUN_TIME). This ensures the measurement window only
counts time when both tasks are fully configured and competing.

[1] https://github.com/kernel-patches/bpf/actions/runs/21961895809/job/63442490449

Fixes: be621a76341c ("selftests/sched_ext: Add test for sched_ext dl_server")
Assisted-by: claude-opus-4-6-v1
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

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Merge tag 'sched-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler updates from Ingo Molnar:
"Scheduler Kconfig space updates:

- Further consolidate confi

Merge tag 'sched-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler updates from Ingo Molnar:
"Scheduler Kconfig space updates:

- Further consolidate configurable preemption modes (Peter Zijlstra)

Reduce the number of architectures that are allowed to offer
PREEMPT_NONE and PREEMPT_VOLUNTARY, reducing the number of
preemption models from four to just two: 'full' and 'lazy' on
up-to-date architectures (arm64, loongarch, powerpc, riscv, s390,
x86).

None and voluntary are only available as legacy features on
platforms that don't implement lazy preemption yet, or which don't
even support preemption.

The goal is to eventually remove cond_resched() and voluntary
preemption altogether.

RSEQ based 'scheduler time slice extension' support (Thomas Gleixner
and Peter Zijlstra):

This allows a thread to request a time slice extension when it enters
a critical section to avoid contention on a resource when the thread
is scheduled out inside of the critical section.

- Add fields and constants for time slice extension
- Provide static branch for time slice extensions
- Add statistics for time slice extensions
- Add prctl() to enable time slice extensions
- Implement sys_rseq_slice_yield()
- Implement syscall entry work for time slice extensions
- Implement time slice extension enforcement timer
- Reset slice extension when scheduled
- Implement rseq_grant_slice_extension()
- entry: Hook up rseq time slice extension
- selftests: Implement time slice extension test
- Allow registering RSEQ with slice extension
- Move slice_ext_nsec to debugfs
- Lower default slice extension
- selftests/rseq: Add rseq slice histogram script

Scheduler performance/scalability improvements:

- Update rq->avg_idle when a task is moved to an idle CPU, which
improves the scalability of various workloads (Shubhang Kaushik)

- Reorder fields in 'struct rq' for better caching (Blake Jones)

- Fair scheduler SMP NOHZ balancing code speedups (Shrikanth Hegde):
- Move checking for nohz cpus after time check
- Change likelyhood of nohz.nr_cpus
- Remove nohz.nr_cpus and use weight of cpumask instead

- Avoid false sharing for sched_clock_irqtime (Wangyang Guo)

- Cleanups (Yury Norov):
- Drop useless cpumask_empty() in find_energy_efficient_cpu()
- Simplify task_numa_find_cpu()
- Use cpumask_weight_and() in sched_balance_find_dst_group()

DL scheduler updates:

- Add a deadline server for sched_ext tasks (by Andrea Righi and Joel
Fernandes, with fixes by Peter Zijlstra)

RT scheduler updates:

- Skip currently executing CPU in rto_next_cpu() (Chen Jinghuang)

Entry code updates and performance improvements (Jinjie Ruan)

This is part of the scheduler tree in this cycle due to inter-
dependencies with the RSEQ based time slice extension work:

- Remove unused syscall argument from syscall_trace_enter()
- Rework syscall_exit_to_user_mode_work() for architecture reuse
- Add arch_ptrace_report_syscall_entry/exit()
- Inline syscall_exit_work() and syscall_trace_enter()

Scheduler core updates (Peter Zijlstra):

- Rework sched_class::wakeup_preempt() and rq_modified_*()
- Avoid rq->lock bouncing in sched_balance_newidle()
- Rename rcu_dereference_check_sched_domain() =>
rcu_dereference_sched_domain()
- <linux/compiler_types.h>: Add the __signed_scalar_typeof() helper

Fair scheduler updates/refactoring (Peter Zijlstra and Ingo Molnar):

- Fold the sched_avg update
- Change rcu_dereference_check_sched_domain() to rcu-sched
- Switch to rcu_dereference_all()
- Remove superfluous rcu_read_lock()
- Limit hrtick work
- Join two #ifdef CONFIG_FAIR_GROUP_SCHED blocks
- Clean up comments in 'struct cfs_rq'
- Separate se->vlag from se->vprot
- Rename cfs_rq::avg_load to cfs_rq::sum_weight
- Rename cfs_rq::avg_vruntime to ::sum_w_vruntime & helper functions
- Introduce and use the vruntime_cmp() and vruntime_op() wrappers for
wrapped-signed aritmetics
- Sort out 'blocked_load*' namespace noise

Scheduler debugging code updates:

- Export hidden tracepoints to modules (Gabriele Monaco)

- Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()
(Fushuai Wang)

- Add assertions to QUEUE_CLASS (Peter Zijlstra)

- hrtimer: Fix tracing oddity (Thomas Gleixner)

Misc fixes and cleanups:

- Re-evaluate scheduling when migrating queued tasks out of throttled
cgroups (Zicheng Qu)

- Remove task_struct->faults_disabled_mapping (Christoph Hellwig)

- Fix math notation errors in avg_vruntime comment (Zhan Xusheng)

- sched/cpufreq: Use %pe format for PTR_ERR() printing
(zenghongling)"

* tag 'sched-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (64 commits)
sched: Re-evaluate scheduling when migrating queued tasks out of throttled cgroups
sched/cpufreq: Use %pe format for PTR_ERR() printing
sched/rt: Skip currently executing CPU in rto_next_cpu()
sched/clock: Avoid false sharing for sched_clock_irqtime
selftests/sched_ext: Add test for DL server total_bw consistency
selftests/sched_ext: Add test for sched_ext dl_server
sched/debug: Fix dl_server (re)start conditions
sched/debug: Add support to change sched_ext server params
sched_ext: Add a DL server for sched_ext tasks
sched/debug: Stop and start server based on if it was active
sched/debug: Fix updating of ppos on server write ops
sched/deadline: Clear the defer params
entry: Inline syscall_exit_work() and syscall_trace_enter()
entry: Add arch_ptrace_report_syscall_entry/exit()
entry: Rework syscall_exit_to_user_mode_work() for architecture reuse
entry: Remove unused syscall argument from syscall_trace_enter()
sched: remove task_struct->faults_disabled_mapping
sched: Update rq->avg_idle when a task is moved to an idle CPU
selftests/rseq: Add rseq slice histogram script
hrtimer: Fix trace oddity
...

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selftests/sched_ext: Add test for sched_ext dl_server

Add a selftest to validate the correct behavior of the deadline server
for the ext_sched_class.

Co-developed-by: Joel Fernandes <joelagnelf@nvi

selftests/sched_ext: Add test for sched_ext dl_server

Add a selftest to validate the correct behavior of the deadline server
for the ext_sched_class.

Co-developed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260126100050.3854740-7-arighi@nvidia.com

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