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[qemu/ar7.git] / scripts / kvm / kvm_flightrecorder
blob54a56745e429446405f0cf70e7e5ea4a2d79b7cb
1 #!/usr/bin/env python
3 # KVM Flight Recorder - ring buffer tracing script
5 # Copyright (C) 2012 IBM Corp
7 # Author: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
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:
13 # sudo kvm_flightrecorder start 8192 # 8 MB per-cpu ring buffers
15 # The per-cpu ring buffer size can be given in KB as an optional argument to
16 # the 'start' subcommand.
18 # To stop the flight recorder:
20 # sudo kvm_flightrecorder stop
22 # To dump the contents of the flight recorder (this can be done when the
23 # recorder is stopped or while it is running):
25 # sudo kvm_flightrecorder dump >/path/to/dump.txt
27 # To observe the trace while it is running, use the 'tail' subcommand:
29 # sudo kvm_flightrecorder tail
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.
35 from __future__ import print_function
36 import sys
37 import os
39 tracing_dir = '/sys/kernel/debug/tracing'
41 def trace_path(*args):
42 return os.path.join(tracing_dir, *args)
44 def write_file(path, data):
45 open(path, 'wb').write(data)
47 def enable_event(subsystem, event, enable):
48 write_file(trace_path('events', subsystem, event, 'enable'), '1' if enable else '0')
50 def enable_subsystem(subsystem, enable):
51 write_file(trace_path('events', subsystem, 'enable'), '1' if enable else '0')
53 def start_tracing():
54 enable_subsystem('kvm', True)
55 write_file(trace_path('tracing_on'), '1')
57 def 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')
63 def 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
73 def tail_trace():
74 try:
75 for line in open(trace_path('trace_pipe'), 'r'):
76 sys.stdout.write(line)
77 except KeyboardInterrupt:
78 pass
80 def 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)
85 def main():
86 if len(sys.argv) < 2:
87 usage()
89 cmd = sys.argv[1]
90 if cmd == '--version':
91 print('kvm_flightrecorder version 1.0')
92 sys.exit(0)
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)
102 if cmd == 'start':
103 stop_tracing() # clean up first
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)
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()
126 if __name__ == '__main__':
127 sys.exit(main())