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sched_ext: Don't deliver duplicate ops.cgroup_set_idle() for same value

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ops.cgroup_set_idle() is documented to be invoked when a cgroup
transitions between idle and non-idle states, and scx_group_set_weight()
already skips value-preserving writes. scx_group_set_idle() delivers
every write unconditionally, so rewriting an already-correct cpu.idle
value feeds the BPF scheduler a transition callback each time, which
toggle- or accounting-based schedulers miscount. Mirror the weight
guard and only deliver on an actual change.

Verified with a probe scheduler printing each callback: rewriting
cpu.idle=1 twice on an already-idle cgroup delivered two callbacks
before and none after.

Fixes: 347ed2d566 ("sched/ext: Implement cgroup_set_idle() callback")
Link: https://lore.kernel.org/r/b53c61a1-4d7d-4232-941f-d48b0563d4ed@linux.dev
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tao Cui 2026-09-01 20:43:47 +08:00 committed by Tejun Heo
parent 93d88ac4a4
commit 29871903f3
1 changed files with 2 additions and 1 deletions
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3
kernel/sched/ext/ext.c
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@ -4933,7 +4933,8 @@ void scx_group_set_idle(struct task_group *tg, bool idle)
percpu_down_read(&scx_cgroup_ops_rwsem);
sch = scx_tg_knob_sched(tg);
if (scx_cgroup_enabled && sch && SCX_HAS_OP(sch, cgroup_set_idle))
if (scx_cgroup_enabled && sch && SCX_HAS_OP(sch, cgroup_set_idle) &&
tg->scx.idle != idle)
SCX_CALL_OP(sch, cgroup_set_idle, NULL, tg_cgrp(tg), idle);
/* Update the task group's idle state */