#!/usr/bin/python
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#
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# sync_timing.py Trace time between syncs.
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# For Linux, uses BCC, eBPF. Embedded C.
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#
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# Written as a basic example of tracing time between events.
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#
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# Copyright 2016 Netflix, Inc.
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# Licensed under the Apache License, Version 2.0 (the "License")
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from __future__ import print_function
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from bcc import BPF
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# load BPF program
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b = BPF(text="""
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#include <uapi/linux/ptrace.h>
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BPF_HASH(last);
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int do_trace(struct pt_regs *ctx) {
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u64 ts, *tsp, delta, key = 0;
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// attempt to read stored timestamp
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tsp = last.lookup(&key);
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if (tsp != 0) {
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delta = bpf_ktime_get_ns() - *tsp;
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if (delta < 1000000000) {
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// output if time is less than 1 second
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bpf_trace_printk("%d\\n", delta / 1000000);
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}
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last.delete(&key);
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}
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// update stored timestamp
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ts = bpf_ktime_get_ns();
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last.update(&key, &ts);
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return 0;
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}
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""")
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b.attach_kprobe(event=b.get_syscall_fnname("sync"), fn_name="do_trace")
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print("Tracing for quick sync's... Ctrl-C to end")
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# format output
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start = 0
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while 1:
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(task, pid, cpu, flags, ts, ms) = b.trace_fields()
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if start == 0:
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start = ts
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ts = ts - start
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print("At time %.2f s: multiple syncs detected, last %s ms ago" % (ts, ms))
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