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      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 
     11 from __future__ import print_function
     12 from bcc import BPF
     13 
     14 # load BPF program
     15 b = BPF(text="""
     16 #include <uapi/linux/ptrace.h>
     17 
     18 BPF_HASH(last);
     19 
     20 int do_trace(struct pt_regs *ctx) {
     21     u64 ts, *tsp, delta, key = 0;
     22 
     23     // attempt to read stored timestamp
     24     tsp = last.lookup(&key);
     25     if (tsp != 0) {
     26         delta = bpf_ktime_get_ns() - *tsp;
     27         if (delta < 1000000000) {
     28             // output if time is less than 1 second
     29             bpf_trace_printk("%d\\n", delta / 1000000);
     30         }
     31         last.delete(&key);
     32     }
     33 
     34     // update stored timestamp
     35     ts = bpf_ktime_get_ns();
     36     last.update(&key, &ts);
     37     return 0;
     38 }
     39 """)
     40 
     41 b.attach_kprobe(event=b.get_syscall_fnname("sync"), fn_name="do_trace")
     42 print("Tracing for quick sync's... Ctrl-C to end")
     43 
     44 # format output
     45 start = 0
     46 while 1:
     47     (task, pid, cpu, flags, ts, ms) = b.trace_fields()
     48     if start == 0:
     49         start = ts
     50     ts = ts - start
     51     print("At time %.2f s: multiple syncs detected, last %s ms ago" % (ts, ms))
     52