1#!/usr/bin/python 2# 3# sync_timing.py Trace time between syncs. 4# For Linux, uses BCC, eBPF. Embedded C. 5# 6# Written as a basic example of tracing time between events. 7# 8# Copyright 2016 Netflix, Inc. 9# Licensed under the Apache License, Version 2.0 (the "License") 10 11from __future__ import print_function 12from bcc import BPF 13from bcc.utils import printb 14 15# load BPF program 16b = BPF(text=""" 17#include <uapi/linux/ptrace.h> 18 19BPF_HASH(last); 20 21int do_trace(struct pt_regs *ctx) { 22 u64 ts, *tsp, delta, key = 0; 23 24 // attempt to read stored timestamp 25 tsp = last.lookup(&key); 26 if (tsp != NULL) { 27 delta = bpf_ktime_get_ns() - *tsp; 28 if (delta < 1000000000) { 29 // output if time is less than 1 second 30 bpf_trace_printk("%d\\n", delta / 1000000); 31 } 32 last.delete(&key); 33 } 34 35 // update stored timestamp 36 ts = bpf_ktime_get_ns(); 37 last.update(&key, &ts); 38 return 0; 39} 40""") 41 42b.attach_kprobe(event=b.get_syscall_fnname("sync"), fn_name="do_trace") 43print("Tracing for quick sync's... Ctrl-C to end") 44 45# format output 46start = 0 47while 1: 48 try: 49 (task, pid, cpu, flags, ts, ms) = b.trace_fields() 50 if start == 0: 51 start = ts 52 ts = ts - start 53 printb(b"At time %.2f s: multiple syncs detected, last %s ms ago" % (ts, ms)) 54 except KeyboardInterrupt: 55 exit() 56