profiling: introduce a "profiling.time-track" option

This option allows to switch the time used by the statistical profiler from
cpu to real time. Our goal is to profile IO intensive operations using the
mercurial profiler.

mercurial/configitems.py

@@ -867,6 +867,9 coreconfigitem('profiling', 'sort',
 coreconfigitem('profiling', 'statformat',
     default='hotpath',
 )
+coreconfigitem('profiling', 'time-track',
+    default='cpu',
+)
 coreconfigitem('profiling', 'type',
     default='stat',
 )

mercurial/help/config.txt

@@ -1652,6 +1652,10 statistical text report generated from t
     ``inlinetime``.
     (default: inlinetime)
 
+``time-track``
+    Control if the stat profiler track ``cpu`` or ``real`` time.
+    (default: ``cpu``)
+
 ``limit``
     Number of lines to show. Specific to the ``ls`` instrumenting profiler.
     (default: 30)

mercurial/profiling.py

@@ -101,7 +101,8 def statprofile(ui, fp):
     else:
         ui.warn(_("invalid sampling frequency '%s' - ignoring\n") % freq)
 
-    statprof.start(mechanism='thread')
+    track = ui.config('profiling', 'time-track')
+    statprof.start(mechanism='thread', track=track)
 
     try:
         yield

mercurial/statprof.py

@@ -148,6 +148,7 def clock():
 class ProfileState(object):
     def __init__(self, frequency=None):
         self.reset(frequency)
+        self.track = 'cpu'
 
     def reset(self, frequency=None):
         # total so far
@@ -180,7 +181,13 class ProfileState(object):
         )
 
     def seconds_per_sample(self):
-        return self.accumulated_time[0] / len(self.samples)
+        return self.accumulated_time[self.timeidx] / len(self.samples)
+
+    @property
+    def timeidx(self):
+        if self.track == 'real':
+            return 1
+        return 0
 
 state = ProfileState()
 
@@ -268,7 +275,8 def profile_signal_handler(signum, frame
         now = clock()
         state.accumulate_time(now)
 
-        state.samples.append(Sample.from_frame(frame, state.accumulated_time[0]))
+        timestamp = state.accumulated_time[state.timeidx]
+        state.samples.append(Sample.from_frame(frame, timestamp))
 
         signal.setitimer(signal.ITIMER_PROF,
             state.sample_interval, 0.0)
@@ -281,7 +289,9 def samplerthread(tid):
         state.accumulate_time(now)
 
         frame = sys._current_frames()[tid]
-        state.samples.append(Sample.from_frame(frame, state.accumulated_time[0]))
+
+        timestamp = state.accumulated_time[state.timeidx]
+        state.samples.append(Sample.from_frame(frame, timestamp))
 
         state.last_start_time = now
         time.sleep(state.sample_interval)
@@ -295,8 +305,9 def is_active():
     return state.profile_level > 0
 
 lastmechanism = None
-def start(mechanism='thread'):
+def start(mechanism='thread', track='cpu'):
     '''Install the profiling signal handler, and start profiling.'''
+    state.track = track # note: nesting different mode won't work
     state.profile_level += 1
     if state.profile_level == 1:
         state.last_start_time = clock()