[PATCH v5 00/14] Add a deadline server for sched_ext tasks

Joel Fernandes
2025-06-20T20:32:48Z

sched_ext tasks currently are starved by RT hoggers especially since RT
throttling was replaced by deadline servers to boost only CFS tasks. Several
users in the community have reported issues with RT stalling sched_ext tasks.
Add a sched_ext deadline server as well so that sched_ext tasks are also
boosted and do not suffer starvation.

A kselftest is also provided to verify the starvation issues are now fixed.

Btw, there is still something funky going on with CPU hotplug and the
relinquish patch. Sometimes the sched_ext's hotplug self-test locks up
(./runner -t hotplug). Reverting that patch fixes it, so I am suspecting
something is off in dl_server_remove_params() when it is being called on
offline CPUs.

v4->v5:
- Added a kselftest (total_bw) to sched_ext to verify bandwidth values
from debugfs.
- Address comment from Andrea about redundant rq clock invalidation.

v3->v4:
- Fixed issues with hotplugged CPUs having their DL server bandwidth
altered due to loading SCX.
- Fixed other issues.
- Rebased on Linus master.
- All sched_ext kselftests reliably pass now, also verified that
the total_bw in debugfs (CONFIG_SCHED_DEBUG) is conserved with
these patches.

v2->v3:
- Removed code duplication in debugfs. Made ext interface separate.
- Fixed issue where rq_lock_irqsave was not used in the relinquish patch.
- Fixed running bw accounting issue in dl_server_remove_params.

Link to v1: https://lore.kernel.org/all/20250315022158.2354454-1-joelagnelf@nvidia.com/
Link to v2: https://lore.kernel.org/all/20250602180110.816225-1-joelagnelf@nvidia.com/
Link to v3: https://lore.kernel.org/all/20250613051734.4023260-1-joelagnelf@nvidia.com/
Link to v4: https://lore.kernel.org/all/20250617200523.1261231-1-joelagnelf@nvidia.com/

Andrea Righi (2):
sched/deadline: Add support to remove DLserver's bandwidth
contribution
selftests/sched_ext: Add test for sched_ext dl_server

Joel Fernandes (12):
sched/debug: Fix updating of ppos on server write ops
sched/debug: Stop and start server based on if it was active
sched/deadline: Clear the defer params
sched/deadline: Prevent setting server as started if params couldn't
be applied
sched/deadline: Return EBUSY if dl_bw_cpus is zero
sched: Add support to pick functions to take rf
sched: Add a server arg to dl_server_update_idle_time()
sched/ext: Add a DL server for sched_ext tasks
sched/debug: Add support to change sched_ext server params
sched/ext: Relinquish DL server reservations when not needed
sched/deadline: Fix DL server crash in inactive_timer callback
selftests/sched_ext: Add test for DL server total_bw consistency

include/linux/sched.h | 2 +-
kernel/sched/core.c | 19 +-
kernel/sched/deadline.c | 84 +++--
kernel/sched/debug.c | 171 +++++++++--
kernel/sched/ext.c | 120 +++++++-
kernel/sched/fair.c | 15 +-
kernel/sched/idle.c | 4 +-
kernel/sched/rt.c | 2 +-
kernel/sched/sched.h | 13 +-
kernel/sched/stop_task.c | 2 +-
tools/testing/selftests/sched_ext/Makefile | 2 +
.../selftests/sched_ext/rt_stall.bpf.c | 23 ++
tools/testing/selftests/sched_ext/rt_stall.c | 213 +++++++++++++
tools/testing/selftests/sched_ext/total_bw.c | 286 ++++++++++++++++++
14 files changed, 872 insertions(+), 84 deletions(-)
create mode 100644 tools/testing/selftests/sched_ext/rt_stall.bpf.c
create mode 100644 tools/testing/selftests/sched_ext/rt_stall.c
create mode 100644 tools/testing/selftests/sched_ext/total_bw.c

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2.43.0