runqslower.py

#!/usr/bin/env python
# @lint-avoid-python-3-compatibility-imports
#
# runqslower    Trace long process scheduling delays.
#               For Linux, uses BCC, eBPF.
#
# This script traces high scheduling delays between tasks being
# ready to run and them running on CPU after that.
#
# USAGE: runqslower [-p PID] [-t TID] [-P] [min_us]
#
# REQUIRES: Linux 4.9+ (BPF_PROG_TYPE_PERF_EVENT support).
#
# This measures the time a task spends waiting on a run queue for a turn
# on-CPU, and shows this time as a individual events. This time should be small,
# but a task may need to wait its turn due to CPU load.
#
# This measures two types of run queue latency:
# 1. The time from a task being enqueued on a run queue to its context switch
#    and execution. This traces ttwu_do_wakeup(), wake_up_new_task() ->
#    finish_task_switch() with either raw tracepoints (if supported) or kprobes
#    and instruments the run queue latency after a voluntary context switch.
# 2. The time from when a task was involuntary context switched and still
#    in the runnable state, to when it next executed. This is instrumented
#    from finish_task_switch() alone.
#
# Copyright 2016 Cloudflare, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 02-May-2018   Ivan Babrou   Created this.
# 18-Nov-2019   Gergely Bod   BUG fix: Use bpf_probe_read_kernel_str() to extract the
#                               process name from 'task_struct* next' in raw tp code.
#                               bpf_get_current_comm() operates on the current task
#                               which might already be different than 'next'.

from __future__ import print_function
from bcc import BPF
import argparse
from time import strftime

# arguments
examples = """examples:
    ./runqslower         # trace run queue latency higher than 10000 us (default)
    ./runqslower 1000    # trace run queue latency higher than 1000 us
    ./runqslower -p 123  # trace pid 123
    ./runqslower -t 123  # trace tid 123 (use for threads only)
    ./runqslower -P      # also show previous task comm and TID
"""
parser = argparse.ArgumentParser(
    description="Trace high run queue latency",
    formatter_class=argparse.RawDescriptionHelpFormatter,
    epilog=examples)
parser.add_argument("min_us", nargs="?", default='10000',
    help="minimum run queue latency to trace, in us (default 10000)")
parser.add_argument("--ebpf", action="store_true",
    help=argparse.SUPPRESS)

thread_group = parser.add_mutually_exclusive_group()
thread_group.add_argument("-p", "--pid", metavar="PID", dest="pid",
    help="trace this PID only", type=int)
thread_group.add_argument("-t", "--tid", metavar="TID", dest="tid",
    help="trace this TID only", type=int)
thread_group.add_argument("-P", "--previous", action="store_true",
    help="also show previous task name and TID")
args = parser.parse_args()

min_us = int(args.min_us)
debug = 0

# define BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>
#include <linux/sched.h>
#include <linux/nsproxy.h>
#include <linux/pid_namespace.h>

BPF_HASH(start, u32);

struct data_t {
    u32 pid;
    u32 prev_pid;
    char task[TASK_COMM_LEN];
    char prev_task[TASK_COMM_LEN];
    u64 delta_us;
};

BPF_PERF_OUTPUT(events);

// record enqueue timestamp
static int trace_enqueue(u32 tgid, u32 pid)
{
    if (FILTER_PID || FILTER_TGID || pid == 0)
        return 0;
    u64 ts = bpf_ktime_get_ns();
    start.update(&pid, &ts);
    return 0;
}
"""

bpf_text_kprobe = """
int trace_wake_up_new_task(struct pt_regs *ctx, struct task_struct *p)
{
    return trace_enqueue(p->tgid, p->pid);
}

int trace_ttwu_do_wakeup(struct pt_regs *ctx, struct rq *rq, struct task_struct *p,
    int wake_flags)
{
    return trace_enqueue(p->tgid, p->pid);
}

// calculate latency
int trace_run(struct pt_regs *ctx, struct task_struct *prev)
{
    u32 pid, tgid;

    // ivcsw: treat like an enqueue event and store timestamp
    if (prev->STATE_FIELD == TASK_RUNNING) {
        tgid = prev->tgid;
        pid = prev->pid;
        u64 ts = bpf_ktime_get_ns();
        if (pid != 0) {
            if (!(FILTER_PID) && !(FILTER_TGID)) {
                start.update(&pid, &ts);
            }
        }
    }

    pid = bpf_get_current_pid_tgid();

    u64 *tsp, delta_us;

    // fetch timestamp and calculate delta
    tsp = start.lookup(&pid);
    if (tsp == 0) {
        return 0;   // missed enqueue
    }
    delta_us = (bpf_ktime_get_ns() - *tsp) / 1000;

    if (FILTER_US)
        return 0;

    struct data_t data = {};
    data.pid = pid;
    data.prev_pid = prev->pid;
    data.delta_us = delta_us;
    bpf_get_current_comm(&data.task, sizeof(data.task));
    bpf_probe_read_kernel_str(&data.prev_task, sizeof(data.prev_task), prev->comm);

    // output
    events.perf_submit(ctx, &data, sizeof(data));

    start.delete(&pid);
    return 0;
}
"""

bpf_text_raw_tp = """
RAW_TRACEPOINT_PROBE(sched_wakeup)
{
    // TP_PROTO(struct task_struct *p)
    struct task_struct *p = (struct task_struct *)ctx->args[0];
    return trace_enqueue(p->tgid, p->pid);
}

RAW_TRACEPOINT_PROBE(sched_wakeup_new)
{
    // TP_PROTO(struct task_struct *p)
    struct task_struct *p = (struct task_struct *)ctx->args[0];
    u32 tgid, pid;

    bpf_probe_read_kernel(&tgid, sizeof(tgid), &p->tgid);
    bpf_probe_read_kernel(&pid, sizeof(pid), &p->pid);
    return trace_enqueue(tgid, pid);
}

RAW_TRACEPOINT_PROBE(sched_switch)
{
    // TP_PROTO(bool preempt, struct task_struct *prev, struct task_struct *next)
    struct task_struct *prev = (struct task_struct *)ctx->args[1];
    struct task_struct *next= (struct task_struct *)ctx->args[2];
    u32 tgid, pid;
    long state;

    // ivcsw: treat like an enqueue event and store timestamp
    bpf_probe_read_kernel(&state, sizeof(long), (const void *)&prev->STATE_FIELD);
    bpf_probe_read_kernel(&pid, sizeof(prev->pid), &prev->pid);
    if (state == TASK_RUNNING) {
        bpf_probe_read_kernel(&tgid, sizeof(prev->tgid), &prev->tgid);
        u64 ts = bpf_ktime_get_ns();
        if (pid != 0) {
            if (!(FILTER_PID) && !(FILTER_TGID)) {
                start.update(&pid, &ts);
            }
        }

    }

    u32 prev_pid;
    u64 *tsp, delta_us;

    prev_pid = pid;
    bpf_probe_read_kernel(&pid, sizeof(next->pid), &next->pid);

    // fetch timestamp and calculate delta
    tsp = start.lookup(&pid);
    if (tsp == 0) {
        return 0;   // missed enqueue
    }
    delta_us = (bpf_ktime_get_ns() - *tsp) / 1000;

    if (FILTER_US)
        return 0;

    struct data_t data = {};
    data.pid = pid;
    data.prev_pid = prev_pid;
    data.delta_us = delta_us;
    bpf_probe_read_kernel_str(&data.task, sizeof(data.task), next->comm);
    bpf_probe_read_kernel_str(&data.prev_task, sizeof(data.prev_task), prev->comm);

    // output
    events.perf_submit(ctx, &data, sizeof(data));

    start.delete(&pid);
    return 0;
}
"""

is_support_raw_tp = BPF.support_raw_tracepoint()
if is_support_raw_tp:
    bpf_text += bpf_text_raw_tp
else:
    bpf_text += bpf_text_kprobe

# code substitutions
if BPF.kernel_struct_has_field(b'task_struct', b'__state') == 1:
    bpf_text = bpf_text.replace('STATE_FIELD', '__state')
else:
    bpf_text = bpf_text.replace('STATE_FIELD', 'state')
if min_us == 0:
    bpf_text = bpf_text.replace('FILTER_US', '0')
else:
    bpf_text = bpf_text.replace('FILTER_US', 'delta_us <= %s' % str(min_us))

if args.tid:
    bpf_text = bpf_text.replace('FILTER_PID', 'pid != %s' % args.tid)
else:
    bpf_text = bpf_text.replace('FILTER_PID', '0')

if args.pid:
    bpf_text = bpf_text.replace('FILTER_TGID', 'tgid != %s' % args.pid)
else:
    bpf_text = bpf_text.replace('FILTER_TGID', '0')

if debug or args.ebpf:
    print(bpf_text)
    if args.ebpf:
        exit()

# process event
def print_event(cpu, data, size):
    event = b["events"].event(data)
    if args.previous:
        print("%-8s %-16s %-6s %14s %-16s %-6s" % (strftime("%H:%M:%S"), event.task, event.pid, event.delta_us, event.prev_task, event.prev_pid))
    else:
        print("%-8s %-16s %-6s %14s" % (strftime("%H:%M:%S"), event.task, event.pid, event.delta_us))

# load BPF program
b = BPF(text=bpf_text)
if not is_support_raw_tp:
    b.attach_kprobe(event="ttwu_do_wakeup", fn_name="trace_ttwu_do_wakeup")
    b.attach_kprobe(event="wake_up_new_task", fn_name="trace_wake_up_new_task")
    b.attach_kprobe(event_re="^finish_task_switch$|^finish_task_switch\.isra\.\d$",
                    fn_name="trace_run")

print("Tracing run queue latency higher than %d us" % min_us)
if args.previous:
    print("%-8s %-16s %-6s %14s %-16s %-6s" % ("TIME", "COMM", "TID", "LAT(us)", "PREV COMM", "PREV TID"))
else:
    print("%-8s %-16s %-6s %14s" % ("TIME", "COMM", "TID", "LAT(us)"))

# read events
b["events"].open_perf_buffer(print_event, page_cnt=64)
while 1:
    try:
        b.perf_buffer_poll()
    except KeyboardInterrupt:
        exit()