[PATCH v2 04/11] sched_ext: Add an event, DISPATCH_LOCAL_DSQ_OFFLINE

Changwoo Min
2025-01-26T10:16:42Z

Add a core event, DISPATCH_LOCAL_DSQ_OFFLINE, which represents how many
times a BPF scheduler tries to dispatch to an offlined local DSQ.

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

Signed-off-by: Changwoo Min <changwoo@igalia.com>
---
kernel/sched/ext.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 727b1f8b623e..38cf7ea6c385 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1467,6 +1467,12 @@ struct scx_event_stats {
* the core scheduler code silently picks a fallback CPU.
*/
u64 SELECT_CPU_FALLBACK;
+
+ /*
+ * When dispatching to a local DSQ, the CPU may have gone offline in
+ * the meantime. In this case, the task is bounced to the global DSQ.
+ */
+ u64 DISPATCH_LOCAL_DSQ_OFFLINE;
};

/*
@@ -2654,6 +2660,7 @@ static void dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq,
if (unlikely(!task_can_run_on_remote_rq(p, dst_rq, true))) {
dispatch_enqueue(find_global_dsq(p), p,
enq_flags | SCX_ENQ_CLEAR_OPSS);
+ __scx_add_event(DISPATCH_LOCAL_DSQ_OFFLINE, 1);
return;
}

@@ -5492,6 +5499,7 @@ static void scx_dump_state(struct scx_exit_info *ei, size_t dump_len)

scx_bpf_event_stats(&events, sizeof(events));
scx_dump_event(s, &events, SELECT_CPU_FALLBACK);
+ scx_dump_event(s, &events, DISPATCH_LOCAL_DSQ_OFFLINE);

if (seq_buf_has_overflowed(&s) && dump_len >= sizeof(trunc_marker))
memcpy(ei->dump + dump_len - sizeof(trunc_marker),
@@ -7821,6 +7829,7 @@ __bpf_kfunc void scx_bpf_event_stats(struct scx_event_stats *events,
for_each_possible_cpu(cpu) {
e_cpu = per_cpu_ptr(&event_stats_cpu, cpu);
scx_agg_event(&e_sys, e_cpu, SELECT_CPU_FALLBACK);
+ scx_agg_event(&e_sys, e_cpu, DISPATCH_LOCAL_DSQ_OFFLINE);
}

/*
--
2.48.1