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![Stefan Hajnoczi](/assets/img/avatar_default.png)
Trace events outside the global mutex cannot be used with the simple trace backend since it is not thread-safe. There is no check to prevent them being enabled so people sometimes learn this the hard way. This patch restructures the simple trace backend with a ring buffer suitable for multiple concurrent writers. A writeout thread empties the trace buffer when threshold fill levels are reached. Should the writeout thread be unable to keep up with trace generation, records will simply be dropped. Each time events are dropped a special record is written to the trace file indicating how many events were dropped. The event ID is 0xfffffffffffffffe and its signature is dropped(uint32_t count). Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
152 lines
4.6 KiB
Python
Executable file
152 lines
4.6 KiB
Python
Executable file
#!/usr/bin/env python
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#
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# Pretty-printer for simple trace backend binary trace files
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#
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# Copyright IBM, Corp. 2010
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#
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# This work is licensed under the terms of the GNU GPL, version 2. See
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# the COPYING file in the top-level directory.
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#
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# For help see docs/tracing.txt
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import struct
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import re
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import inspect
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header_event_id = 0xffffffffffffffff
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header_magic = 0xf2b177cb0aa429b4
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header_version = 0
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dropped_event_id = 0xfffffffffffffffe
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trace_fmt = '=QQQQQQQQ'
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trace_len = struct.calcsize(trace_fmt)
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event_re = re.compile(r'(disable\s+)?([a-zA-Z0-9_]+)\(([^)]*)\).*')
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def parse_events(fobj):
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"""Parse a trace-events file into {event_num: (name, arg1, ...)}."""
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def get_argnames(args):
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"""Extract argument names from a parameter list."""
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return tuple(arg.split()[-1].lstrip('*') for arg in args.split(','))
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events = {dropped_event_id: ('dropped', 'count')}
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event_num = 0
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for line in fobj:
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m = event_re.match(line.strip())
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if m is None:
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continue
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disable, name, args = m.groups()
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events[event_num] = (name,) + get_argnames(args)
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event_num += 1
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return events
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def read_record(fobj):
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"""Deserialize a trace record from a file into a tuple (event_num, timestamp, arg1, ..., arg6)."""
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s = fobj.read(trace_len)
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if len(s) != trace_len:
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return None
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return struct.unpack(trace_fmt, s)
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def read_trace_file(fobj):
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"""Deserialize trace records from a file, yielding record tuples (event_num, timestamp, arg1, ..., arg6)."""
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header = read_record(fobj)
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if header is None or \
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header[0] != header_event_id or \
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header[1] != header_magic or \
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header[2] != header_version:
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raise ValueError('not a trace file or incompatible version')
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while True:
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rec = read_record(fobj)
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if rec is None:
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break
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yield rec
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class Analyzer(object):
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"""A trace file analyzer which processes trace records.
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An analyzer can be passed to run() or process(). The begin() method is
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invoked, then each trace record is processed, and finally the end() method
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is invoked.
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If a method matching a trace event name exists, it is invoked to process
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that trace record. Otherwise the catchall() method is invoked."""
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def begin(self):
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"""Called at the start of the trace."""
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pass
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def catchall(self, event, rec):
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"""Called if no specific method for processing a trace event has been found."""
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pass
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def end(self):
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"""Called at the end of the trace."""
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pass
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def process(events, log, analyzer):
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"""Invoke an analyzer on each event in a log."""
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if isinstance(events, str):
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events = parse_events(open(events, 'r'))
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if isinstance(log, str):
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log = open(log, 'rb')
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def build_fn(analyzer, event):
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fn = getattr(analyzer, event[0], None)
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if fn is None:
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return analyzer.catchall
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event_argcount = len(event) - 1
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fn_argcount = len(inspect.getargspec(fn)[0]) - 1
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if fn_argcount == event_argcount + 1:
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# Include timestamp as first argument
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return lambda _, rec: fn(*rec[1:2 + fn_argcount])
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else:
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# Just arguments, no timestamp
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return lambda _, rec: fn(*rec[2:2 + fn_argcount])
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analyzer.begin()
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fn_cache = {}
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for rec in read_trace_file(log):
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event_num = rec[0]
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event = events[event_num]
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if event_num not in fn_cache:
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fn_cache[event_num] = build_fn(analyzer, event)
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fn_cache[event_num](event, rec)
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analyzer.end()
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def run(analyzer):
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"""Execute an analyzer on a trace file given on the command-line.
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This function is useful as a driver for simple analysis scripts. More
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advanced scripts will want to call process() instead."""
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import sys
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if len(sys.argv) != 3:
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sys.stderr.write('usage: %s <trace-events> <trace-file>\n' % sys.argv[0])
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sys.exit(1)
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events = parse_events(open(sys.argv[1], 'r'))
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process(events, sys.argv[2], analyzer)
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if __name__ == '__main__':
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class Formatter(Analyzer):
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def __init__(self):
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self.last_timestamp = None
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def catchall(self, event, rec):
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timestamp = rec[1]
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if self.last_timestamp is None:
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self.last_timestamp = timestamp
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delta_ns = timestamp - self.last_timestamp
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self.last_timestamp = timestamp
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fields = [event[0], '%0.3f' % (delta_ns / 1000.0)]
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for i in xrange(1, len(event)):
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fields.append('%s=0x%x' % (event[i], rec[i + 1]))
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print ' '.join(fields)
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run(Formatter())
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