scx_lavd: Do not set task's time slice to zero at the ops.enqueue() path #1284
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Note that at ops.enqueue() path, setting a task's slice to zero is risky because we don't know the exact status of the task, so it could cause a zero time slice error as follows: [ 8271.001818] sched_ext: ksoftirqd/1[70] has zero slice in pick_task_scx() The zero slice warning is harmful because the sched_ext core ends up setting the time slice to SCX_SLICE_DFL (20 msec), increasing latency spikes. Thus, we do not set the time slice to 0 at the ops.enqueue() path and rely on scx_bpf_kick_cpu(SCX_KICK_PREEMPT) all the time. Also, use 1 (instead of 0) as a marker to perform scx_bpf_kick_cpu(). This should solve the following issue: sched-ext#1283 Signed-off-by: Changwoo Min <changwoo@igalia.com>
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Separate setting the preemption information into the case of entering into an idle state and the case that the CPU is taken by a high scheduling class. Signed-off-by: Changwoo Min <changwoo@igalia.com>
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Note that at ops.enqueue() path, setting a task's slice to zero is risky because we don't know the exact status of the task, so it could cause a zero time slice error as follows:
[ 8271.001818] sched_ext: ksoftirqd/1[70] has zero slice in pick_task_scx()
The zero slice warning is harmful because the sched_ext core ends up setting the time slice to SCX_SLICE_DFL (20 msec), increasing latency spikes.
Thus, we do not set the time slice to 0 at the ops.enqueue() path and rely on scx_bpf_kick_cpu(SCX_KICK_PREEMPT) all the time. Also, use 1 (instead of 0) as a marker to perform scx_bpf_kick_cpu().
This should solve the following issue:
#1283