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sched_ext: Add an event, SCX_EV_ENQ_SLICE_DFL

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Add a core event, SCX_EV_ENQ_SLICE_DFL, which represents how many
tasks have been enqueued (or pick_task-ed or select_cpu-ed) with
a default time slice (SCX_SLICE_DFL).

Scheduling a task with SCX_SLICE_DFL unintentionally would be a source
of latency spikes because SCX_SLICE_DFL is relatively long (20 msec).
Thus, soaring the SCX_EV_ENQ_SLICE_DFL value would be a sign of BPF
scheduler bugs, causing latency spikes, especially when ops.select_cpu()
is provided.

__scx_add_event() is used since the caller holds an rq lock or p->pi_lock,
so the preemption has already been disabled.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Changwoo Min 2025-02-07 15:40:51 +09:00 committed by Tejun Heo
parent 2494e555fb
commit 6d3f8fb4b2
1 changed files with 15 additions and 1 deletions
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16
kernel/sched/ext.c
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@ -1468,6 +1468,12 @@ struct scx_event_stats {
*/
u64 SCX_EV_ENQ_SKIP_EXITING;
/*
* The total number of tasks enqueued (or pick_task-ed) with a
* default time slice (SCX_SLICE_DFL).
*/
u64 SCX_EV_ENQ_SLICE_DFL;
/*
* The total duration of bypass modes in nanoseconds.
*/
@ -2134,6 +2140,7 @@ static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
*/
touch_core_sched(rq, p);
p->scx.slice = SCX_SLICE_DFL;
__scx_add_event(SCX_EV_ENQ_SLICE_DFL, 1);
local_norefill:
dispatch_enqueue(&rq->scx.local_dsq, p, enq_flags);
return;
@ -2141,6 +2148,7 @@ static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
global:
touch_core_sched(rq, p); /* see the comment in local: */
p->scx.slice = SCX_SLICE_DFL;
__scx_add_event(SCX_EV_ENQ_SLICE_DFL, 1);
dispatch_enqueue(find_global_dsq(p), p, enq_flags);
}
@ -3202,8 +3210,10 @@ static struct task_struct *pick_task_scx(struct rq *rq)
*/
if (keep_prev) {
p = prev;
if (!p->scx.slice)
if (!p->scx.slice) {
p->scx.slice = SCX_SLICE_DFL;
__scx_add_event(SCX_EV_ENQ_SLICE_DFL, 1);
}
} else {
p = first_local_task(rq);
if (!p) {
@ -3219,6 +3229,7 @@ static struct task_struct *pick_task_scx(struct rq *rq)
scx_warned_zero_slice = true;
}
p->scx.slice = SCX_SLICE_DFL;
__scx_add_event(SCX_EV_ENQ_SLICE_DFL, 1);
}
}
@ -3306,6 +3317,7 @@ static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flag
if (found) {
p->scx.slice = SCX_SLICE_DFL;
p->scx.ddsp_dsq_id = SCX_DSQ_LOCAL;
__scx_add_event(SCX_EV_ENQ_SLICE_DFL, 1);
}
if (rq_bypass)
@ -5023,6 +5035,7 @@ static void scx_dump_state(struct scx_exit_info *ei, size_t dump_len)
scx_dump_event(s, &events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE);
scx_dump_event(s, &events, SCX_EV_DISPATCH_KEEP_LAST);
scx_dump_event(s, &events, SCX_EV_ENQ_SKIP_EXITING);
scx_dump_event(s, &events, SCX_EV_ENQ_SLICE_DFL);
scx_dump_event(s, &events, SCX_EV_BYPASS_DURATION);
scx_dump_event(s, &events, SCX_EV_BYPASS_DISPATCH);
scx_dump_event(s, &events, SCX_EV_BYPASS_ACTIVATE);
@ -7163,6 +7176,7 @@ __bpf_kfunc void scx_bpf_events(struct scx_event_stats *events,
scx_agg_event(&e_sys, e_cpu, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE);
scx_agg_event(&e_sys, e_cpu, SCX_EV_DISPATCH_KEEP_LAST);
scx_agg_event(&e_sys, e_cpu, SCX_EV_ENQ_SKIP_EXITING);
scx_agg_event(&e_sys, e_cpu, SCX_EV_ENQ_SLICE_DFL);
scx_agg_event(&e_sys, e_cpu, SCX_EV_BYPASS_DURATION);
scx_agg_event(&e_sys, e_cpu, SCX_EV_BYPASS_DISPATCH);
scx_agg_event(&e_sys, e_cpu, SCX_EV_BYPASS_ACTIVATE);