sched_ext: Add an event, SCX_EV_SELECT_CPU_FALLBACK

Add a core event, SCX_EV_SELECT_CPU_FALLBACK, which represents how many times
ops.select_cpu() returns a CPU that the task can't use.

__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/include/linux/sched/ext.h b/include/linux/sched/ext.h
index 1d70a9867fb12e2a88edf4766fa874628509dbaa..f7545430a54821193bcfecd0a1a21c326cc438b1 100644 (file)
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -146,6 +146,7 @@ struct sched_ext_entity {
        u32                     weight;
        s32                     sticky_cpu;
        s32                     holding_cpu;
+       s32                     selected_cpu;
        u32                     kf_mask;        /* see scx_kf_mask above */
        struct task_struct      *kf_tasks[2];   /* see SCX_CALL_OP_TASK() */
        atomic_long_t           ops_state;

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 4e28e88e88d4813e13e81812fccfc85cfcdb9ff0..f80c8dc024a7a6aa1dbdaf8ba71f351b19803a09 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1444,6 +1444,11 @@ static struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter)
  * Collection of event counters. Event types are placed in descending order.
  */
 struct scx_event_stats {
+       /*
+        * If ops.select_cpu() returns a CPU which can't be used by the task,
+        * the core scheduler code silently picks a fallback CPU.
+        */
+       u64             SCX_EV_SELECT_CPU_FALLBACK;
 };
 
 /*
@@ -2170,6 +2175,10 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags
        do_enqueue_task(rq, p, enq_flags, sticky_cpu);
 out:
        rq->scx.flags &= ~SCX_RQ_IN_WAKEUP;
+
+       if ((enq_flags & SCX_ENQ_CPU_SELECTED) &&
+           unlikely(cpu_of(rq) != p->scx.selected_cpu))
+               __scx_add_event(SCX_EV_SELECT_CPU_FALLBACK, 1);
 }
 
 static void ops_dequeue(struct task_struct *p, u64 deq_flags)
@@ -3240,6 +3249,7 @@ static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flag
 
                cpu = SCX_CALL_OP_TASK_RET(SCX_KF_ENQUEUE | SCX_KF_SELECT_CPU,
                                           select_cpu, p, prev_cpu, wake_flags);
+               p->scx.selected_cpu = cpu;
                *ddsp_taskp = NULL;
                if (ops_cpu_valid(cpu, "from ops.select_cpu()"))
                        return cpu;
@@ -3250,6 +3260,7 @@ static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flag
                s32 cpu;
 
                cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags, &found);
+               p->scx.selected_cpu = cpu;
                if (found) {
                        p->scx.slice = SCX_SLICE_DFL;
                        p->scx.ddsp_dsq_id = SCX_DSQ_LOCAL;
@@ -4957,6 +4968,7 @@ static void scx_dump_state(struct scx_exit_info *ei, size_t dump_len)
        dump_line(&s, "--------------");
 
        scx_bpf_events(&events, sizeof(events));
+       scx_dump_event(s, &events, SCX_EV_SELECT_CPU_FALLBACK);
 
        if (seq_buf_has_overflowed(&s) && dump_len >= sizeof(trunc_marker))
                memcpy(ei->dump + dump_len - sizeof(trunc_marker),
@@ -7090,6 +7102,7 @@ __bpf_kfunc void scx_bpf_events(struct scx_event_stats *events,
        memset(&e_sys, 0, sizeof(e_sys));
        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);
        }
 
        /*