sched_ext: Add an event, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE

Add a core event, SCX_EV_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>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index f80c8dc024a7a6aa1dbdaf8ba71f351b19803a09..d1447f18381ee40e4636a3d46bd7d51ee9d99786 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1449,6 +1449,12 @@ struct scx_event_stats {
         * the core scheduler code silently picks a fallback CPU.
         */
        u64             SCX_EV_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             SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE;
 };
 
 /*
@@ -2643,6 +2649,7 @@ 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(SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE, 1);
                return;
        }
 
@@ -4969,6 +4976,7 @@ static void scx_dump_state(struct scx_exit_info *ei, size_t dump_len)
 
        scx_bpf_events(&events, sizeof(events));
        scx_dump_event(s, &events, SCX_EV_SELECT_CPU_FALLBACK);
+       scx_dump_event(s, &events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE);
 
        if (seq_buf_has_overflowed(&s) && dump_len >= sizeof(trunc_marker))
                memcpy(ei->dump + dump_len - sizeof(trunc_marker),
@@ -7103,6 +7111,7 @@ __bpf_kfunc void scx_bpf_events(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, SCX_EV_SELECT_CPU_FALLBACK);
+               scx_agg_event(&e_sys, e_cpu, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE);
        }
 
        /*