xref: /openbmc/qemu/scripts/kvm/kvm_flightrecorder (revision 503bb0b9) 
1#!/usr/bin/env python
2#
3# KVM Flight Recorder - ring buffer tracing script
4#
5# Copyright (C) 2012 IBM Corp
6#
7# Author: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
8#
9# This script provides a command-line interface to kvm ftrace and is designed
10# to be used as a flight recorder that is always running.  To start in-memory
11# recording:
12#
13# sudo kvm_flightrecorder start 8192  # 8 MB per-cpu ring buffers
14#
15# The per-cpu ring buffer size can be given in KB as an optional argument to
16# the 'start' subcommand.
17#
18# To stop the flight recorder:
19#
20# sudo kvm_flightrecorder stop
21#
22# To dump the contents of the flight recorder (this can be done when the
23# recorder is stopped or while it is running):
24#
25# sudo kvm_flightrecorder dump >/path/to/dump.txt
26#
27# To observe the trace while it is running, use the 'tail' subcommand:
28#
29# sudo kvm_flightrecorder tail
30#
31# Note that the flight recorder may impact overall system performance by
32# consuming CPU cycles.  No disk I/O is performed since the ring buffer holds a
33# fixed-size in-memory trace.
34
35from __future__ import print_function
36import sys
37import os
38
39tracing_dir = '/sys/kernel/debug/tracing'
40
41def trace_path(*args):
42    return os.path.join(tracing_dir, *args)
43
44def write_file(path, data):
45    open(path, 'wb').write(data)
46
47def enable_event(subsystem, event, enable):
48    write_file(trace_path('events', subsystem, event, 'enable'), '1' if enable else '0')
49
50def enable_subsystem(subsystem, enable):
51    write_file(trace_path('events', subsystem, 'enable'), '1' if enable else '0')
52
53def start_tracing():
54    enable_subsystem('kvm', True)
55    write_file(trace_path('tracing_on'), '1')
56
57def stop_tracing():
58    write_file(trace_path('tracing_on'), '0')
59    enable_subsystem('kvm', False)
60    write_file(trace_path('events', 'enable'), '0')
61    write_file(trace_path('current_tracer'), 'nop')
62
63def dump_trace():
64    tracefile = open(trace_path('trace'), 'r')
65    try:
66        lines = True
67        while lines:
68            lines = tracefile.readlines(64 * 1024)
69            sys.stdout.writelines(lines)
70    except KeyboardInterrupt:
71        pass
72
73def tail_trace():
74    try:
75        for line in open(trace_path('trace_pipe'), 'r'):
76            sys.stdout.write(line)
77    except KeyboardInterrupt:
78        pass
79
80def usage():
81    print('Usage: %s start [buffer_size_kb] | stop | dump | tail' % sys.argv[0])
82    print('Control the KVM flight recorder tracing.')
83    sys.exit(0)
84
85def main():
86    if len(sys.argv) < 2:
87        usage()
88
89    cmd = sys.argv[1]
90    if cmd == '--version':
91        print('kvm_flightrecorder version 1.0')
92        sys.exit(0)
93
94    if not os.path.isdir(tracing_dir):
95        print('Unable to tracing debugfs directory, try:')
96        print('mount -t debugfs none /sys/kernel/debug')
97        sys.exit(1)
98    if not os.access(tracing_dir, os.W_OK):
99        print('Unable to write to tracing debugfs directory, please run as root')
100        sys.exit(1)
101
102    if cmd == 'start':
103        stop_tracing() # clean up first
104
105        if len(sys.argv) == 3:
106            try:
107                buffer_size_kb = int(sys.argv[2])
108            except ValueError:
109                print('Invalid per-cpu trace buffer size in KB')
110                sys.exit(1)
111            write_file(trace_path('buffer_size_kb'), str(buffer_size_kb))
112            print('Per-CPU ring buffer size set to %d KB' % buffer_size_kb)
113
114        start_tracing()
115        print('KVM flight recorder enabled')
116    elif cmd == 'stop':
117        stop_tracing()
118        print('KVM flight recorder disabled')
119    elif cmd == 'dump':
120        dump_trace()
121    elif cmd == 'tail':
122        tail_trace()
123    else:
124        usage()
125
126if __name__ == '__main__':
127    sys.exit(main())
128