#!/usr/bin/env bpftrace
// SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0
//
// CPU run queue latency histogram.
// Proves OS-level CPU contention. Healthy: <10us p99.
//
// Usage: sudo bpftrace runqlat.bt

tracepoint:sched:sched_wakeup,
tracepoint:sched:sched_wakeup_new
{
    @qtime[args.pid] = nsecs;
}

tracepoint:sched:sched_switch
{
    if (args.prev_state == 0) {
        // voluntary context switch (prev was TASK_RUNNING)
        @qtime[args.prev_pid] = nsecs;
    }

    $ns = @qtime[args.next_pid];
    if ($ns) {
        @usecs = hist((nsecs - $ns) / 1000);
        delete(@qtime[args.next_pid]);
    }
}

interval:s:5
{
    printf("\n--- Run Queue Latency (us) ---\n");
    print(@usecs);
    clear(@usecs);
}

END
{
    clear(@qtime);
}