twatch.py

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#! /usr/bin/python
# -*- python -*-
# -*- coding: utf-8 -*-
#   twatch - Experimental use of the perf python interface
#   Copyright (C) 2011 Arnaldo Carvalho de Melo <acme@redhat.com>
#
#   This application is free software; you can redistribute it and/or
#   modify it under the terms of the GNU General Public License
#   as published by the Free Software Foundation; version 2.
#
#   This application is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
#   General Public License for more details.

import perf

def main(context_switch = 0, thread = -1):
    cpus = perf.cpu_map()
    threads = perf.thread_map(thread)
    evsel = perf.evsel(type   = perf.TYPE_SOFTWARE,
               config = perf.COUNT_SW_DUMMY,
               task = 1, comm = 1, mmap = 0, freq = 0,
               wakeup_events = 1, watermark = 1,
               sample_id_all = 1, context_switch = context_switch,
               sample_type = perf.SAMPLE_PERIOD | perf.SAMPLE_TID | perf.SAMPLE_CPU)

    """What we want are just the PERF_RECORD_ lifetime events for threads,
     using the default, PERF_TYPE_HARDWARE + PERF_COUNT_HW_CYCLES & freq=1
     (the default), makes perf reenable irq_vectors:local_timer_entry, when
     disabling nohz, not good for some use cases where all we want is to get
     threads comes and goes... So use (perf.TYPE_SOFTWARE, perf_COUNT_SW_DUMMY,
     freq=0) instead."""

    evsel.open(cpus = cpus, threads = threads);
    evlist = perf.evlist(cpus, threads)
    evlist.add(evsel)
    evlist.mmap()
    while True:
        evlist.poll(timeout = -1)
        for cpu in cpus:
            event = evlist.read_on_cpu(cpu)
            if not event:
                continue
            print("cpu: {0}, pid: {1}, tid: {2} {3}".format(event.sample_cpu,
                                                                        event.sample_pid,
                                                                        event.sample_tid,
                                                                        event))

if __name__ == '__main__':
    """
    To test the PERF_RECORD_SWITCH record, pick a pid and replace
    in the following line.

    Example output:

cpu: 3, pid: 31463, tid: 31593 { type: context_switch, next_prev_pid: 31463, next_prev_tid: 31593, switch_out: 1 }
cpu: 1, pid: 31463, tid: 31489 { type: context_switch, next_prev_pid: 31463, next_prev_tid: 31489, switch_out: 1 }
cpu: 2, pid: 31463, tid: 31496 { type: context_switch, next_prev_pid: 31463, next_prev_tid: 31496, switch_out: 1 }
cpu: 3, pid: 31463, tid: 31491 { type: context_switch, next_prev_pid: 31463, next_prev_tid: 31491, switch_out: 0 }

    It is possible as well to use event.misc & perf.PERF_RECORD_MISC_SWITCH_OUT
    to figure out if this is a context switch in or out of the monitored threads.

    If bored, please add command line option parsing support for these options :-)
    """
    # main(context_switch = 1, thread = 31463)
    main()