perf: allow profiling of more than one run

By default, we still profile the first run only. However profiling more run help
to understand side effect from one run to the other. So we add an option to be
able to do so.

contrib/perf.py

@@ -20,7 +20,10 b' Configurations'
 
 ``profile-benchmark``
   Enable profiling for the benchmarked section.
-  (The first iteration is benchmarked)
+  (by default, the first iteration is benchmarked)
+
+``profiled-runs``
+  list of iteration to profile (starting from 0)
 
 ``run-limits``
   Control the number of runs each benchmark will perform. The option value
@@ -318,6 +321,11 b' try:'
     )
     configitem(
         b'perf',
+        b'profiled-runs',
+        default=mercurial.configitems.dynamicdefault,
+    )
+    configitem(
+        b'perf',
         b'run-limits',
         default=mercurial.configitems.dynamicdefault,
         experimental=True,
@@ -354,7 +362,7 b' except TypeError:'
     )
     configitem(
         b'perf',
-        b'profile-benchmark',
+        b'profiled-runs',
         default=mercurial.configitems.dynamicdefault,
     )
     configitem(
@@ -491,9 +499,12 b' def gettimer(ui, opts=None):'
         limits = DEFAULTLIMITS
 
     profiler = None
+    profiled_runs = set()
     if profiling is not None:
         if ui.configbool(b"perf", b"profile-benchmark", False):
-            profiler = profiling.profile(ui)
+            profiler = lambda: profiling.profile(ui)
+            for run in ui.configlist(b"perf", b"profiled-runs", [0]):
+                profiled_runs.add(int(run))
 
     prerun = getint(ui, b"perf", b"pre-run", 0)
     t = functools.partial(
@@ -503,6 +514,7 b' def gettimer(ui, opts=None):'
         limits=limits,
         prerun=prerun,
         profiler=profiler,
+        profiled_runs=profiled_runs,
     )
     return t, fm
 
@@ -547,13 +559,14 b' def _timer('
     limits=DEFAULTLIMITS,
     prerun=0,
     profiler=None,
+    profiled_runs=(0,),
 ):
     gc.collect()
     results = []
     begin = util.timer()
     count = 0
     if profiler is None:
-        profiler = NOOPCTX
+        profiler = lambda: NOOPCTX
     for i in range(prerun):
         if setup is not None:
             setup()
@@ -561,13 +574,16 b' def _timer('
             func()
     keepgoing = True
     while keepgoing:
+        if count in profiled_runs:
+            prof = profiler()
+        else:
+            prof = NOOPCTX
         if setup is not None:
             setup()
         with context():
-            with profiler:
+            with prof:
                 with timeone() as item:
                     r = func()
-        profiler = NOOPCTX
         count += 1
         results.append(item[0])
         cstop = util.timer()

tests/test-contrib-perf.t

@@ -59,8 +59,11 b' perfstatus'
     number of run to perform before starting measurement.
   
   "profile-benchmark"
-    Enable profiling for the benchmarked section. (The first iteration is
-    benchmarked)
+    Enable profiling for the benchmarked section. (by default, the first
+    iteration is benchmarked)
+  
+  "profiled-runs"
+    list of iteration to profile (starting from 0)
   
   "run-limits"
     Control the number of runs each benchmark will perform. The option value