context_switches.bt

#!/usr/bin/env bpftrace
// SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0
//
// Context switch histograms per thread.
// High context switch rates on tokio workers indicate contention or starvation.
//
// Usage: sudo bpftrace context_switches.bt
//        sudo bpftrace -p <PID> context_switches.bt

tracepoint:sched:sched_switch
/comm == "tokio-runtime-w" || args.prev_comm == "tokio-runtime-w"/
{
    if (args.prev_state == 0) {
        // Involuntary: was TASK_RUNNING but got preempted
        @involuntary[args.prev_comm] = count();
    } else {
        // Voluntary: thread yielded or blocked
        @voluntary[args.prev_comm] = count();
    }
}

interval:s:5
{
    printf("\n--- Context Switches (last 5s) ---\n");
    printf("\nVoluntary (thread yielded/blocked):\n");
    print(@voluntary, 10);
    printf("\nInvoluntary (thread preempted while running):\n");
    print(@involuntary, 10);
    clear(@voluntary);
    clear(@involuntary);
}

END
{
    clear(@voluntary);
    clear(@involuntary);
}