Use minimum calibration time rather than avergae to avoid

the illusion of negative run times. Halt with an error if
run times go below 10 ms, indicating that results will be
unreliable.

Tools/pybench/pybench.py

@@ -126,7 +126,7 @@ class Test:
         self.operations = self.operations
         self.rounds = self.rounds
 
-    def run(self):
+    def run(self, cruns):
 
         """ Run the test in two phases: first calibrate, then
             do the actual test. Be careful to keep the calibration
@@ -136,20 +136,23 @@ class Test:
         test = self.test
         calibrate = self.calibrate
         clock = time.clock
-        cruns = self.cruns
         # first calibrate
-        offset = 0.0
+        t = clock()
+        calibrate()
+        offset = clock() - t
         if cruns:
-            for i in range(cruns):
+            for i in range(cruns-1):
                 t = clock()
                 calibrate()
                 t = clock() - t
-                offset = offset + t
-            offset = offset / cruns
+                if t < offset:
+                    offset = t
         # now the real thing
         t = clock()
         test()
         t = clock() - t
+        if t < 0.01:
+            sys.exit("Lower warp required: test times < 10 ms are unreliable")
         self.last_timing = (t-offset,t,offset)
         self.times.append(t-offset)
 
@@ -253,7 +256,7 @@ class Benchmark:
             print len(l), "tests found"
         print
 
-    def run(self, verbose):
+    def run(self, verbose, cruns):
 
         tests = self.tests.items()
         tests.sort()
@@ -266,10 +269,10 @@ class Benchmark:
             if verbose:
                 print ' Round %-25i  real   abs    overhead' % (i+1)
             for j in range(len(tests)):
-                name,t = tests[j]
+                name, t = tests[j]
                 if verbose:
                     print '%30s:' % name,
-                t.run()
+                t.run(cruns)
                 if verbose:
                     print '  %.3fr %.3fa %.3fo' % t.last_timing
             if verbose:
@@ -379,7 +382,7 @@ class PyBenchCmdline(Application):
                SwitchOption('--no-syscheck',
                     '"disable" sys check interval (set to sys.maxint)', 0),
                ArgumentOption('-t', 'tests containing substring', ''),
-               ArgumentOption('-C', 'number of calibration runs (default 0)', '')
+               ArgumentOption('-C', 'number of calibration runs (default 20)', 20)
                ]
 
     about = """\
@@ -423,7 +426,9 @@ python pybench.py -s p15 -c p14
         limitnames = self.values['-t']
         verbose = self.verbose
         nosyscheck = self.values['--no-syscheck']
-
+        cruns = self.values['-C']
+        print "CRUNS:", cruns
+        
         print 'PYBENCH',__version__
 
         # Switch off GC
@@ -488,7 +493,7 @@ python pybench.py -s p15 -c p14
         bench.rounds = rounds
         bench.load_tests(Setup, warp, limitnames, verbose)
         try:
-            bench.run(verbose)
+            bench.run(verbose, cruns)
         except KeyboardInterrupt:
             print
             print '*** KeyboardInterrupt -- Aborting'