sched_ext: scx_qmap - Add rescue support

Browse source

A sched holds only the cids its parent granted and nothing guarantees that
they cover its tasks' affinities. A task that can run on none of them has
nowhere to go and qmap stalls out: it force-inserts the task onto its first
allowed cid, but the kernel bounces the insert back and the task parks in
SHARED_DSQ, which is drained only on self cids it can't run on.

Set SCX_ENQ_RESCUE on these inserts so the kernel diverts such tasks to its
rescue path instead of bouncing them. The force-insert covers scheds with
and without children and fires on re-enqueues, and the SHARED_DSQ scan on
every dispatch rescues tasks stranded there - the enqueue-time check misses
a task whose cids were lost while it was already queued. The wrong-cid fault
injection carries the flag too and doubles as a deterministic rescue-traffic
generator.

-B and -q set the root-only rescue bandwidth and quantum ops knobs. -B 0
maps to SCX_RESCUE_DISABLE and turns rescue off kernel-side. Rescue inserts
are counted and reported in the hier stats line.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

...

This commit is contained in:

Tejun Heo 2026-08-03 11:02:03 -10:00

parent 6206980186

commit e158e309cd

3 changed files with 79 additions and 30 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

85

tools/sched_ext/scx_qmap.bpf.c

View file

23

tools/sched_ext/scx_qmap.c

View file

1

tools/sched_ext/scx_qmap.h

View file