kvm_stat: allow choosing between tracepoints and old stats

The old stats contain information not available in the tracepoints.
By default, keep the old behavior, but allow choosing which set of stats
to present, or even both.

Inspired by a patch from Marcelo Tosatti.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

scripts/kvm/kvm_stat

@@ -352,8 +352,8 @@ class TracepointProvider(object):
         return ret
 
 class Stats:
-    def __init__(self, provider, fields = None):
-        self.provider = provider
+    def __init__(self, providers, fields = None):
+        self.providers = providers
         self.fields_filter = fields
         self._update()
     def _update(self):
@@ -362,22 +362,25 @@ class Stats:
             if not self.fields_filter:
                 return True
             return re.match(self.fields_filter, key) is not None
-        self.values = dict([(key, None)
-                            for key in provider.fields()
-                            if wanted(key)])
-        self.provider.select(self.values.keys())
+        self.values = dict()
+        for d in providers:
+            provider_fields = [key for key in d.fields() if wanted(key)]
+            for key in provider_fields:
+                self.values[key] = None
+            d.select(provider_fields)
     def set_fields_filter(self, fields_filter):
         self.fields_filter = fields_filter
         self._update()
     def get(self):
-        new = self.provider.read()
-        for key in self.provider.fields():
-            oldval = self.values.get(key, (0, 0))
-            newval = new[key]
-            newdelta = None
-            if oldval is not None:
-                newdelta = newval - oldval[0]
-            self.values[key] = (newval, newdelta)
+        for d in providers:
+            new = d.read()
+            for key in d.fields():
+                oldval = self.values.get(key, (0, 0))
+                newval = new[key]
+                newdelta = None
+                if oldval is not None:
+                    newdelta = newval - oldval[0]
+                self.values[key] = (newval, newdelta)
         return self.values
 
 if not os.access('/sys/kernel/debug', os.F_OK):
@@ -487,6 +490,18 @@ options.add_option('-l', '--log',
                    dest = 'log',
                    help = 'run in logging mode (like vmstat)',
                    )
+options.add_option('-t', '--tracepoints',
+                   action = 'store_true',
+                   default = False,
+                   dest = 'tracepoints',
+                   help = 'retrieve statistics from tracepoints',
+                   )
+options.add_option('-d', '--debugfs',
+                   action = 'store_true',
+                   default = False,
+                   dest = 'debugfs',
+                   help = 'retrieve statistics from debugfs',
+                   )
 options.add_option('-f', '--fields',
                    action = 'store',
                    default = None,
@@ -495,12 +510,19 @@ options.add_option('-f', '--fields',
                    )
 (options, args) = options.parse_args(sys.argv)
 
-try:
-    provider = TracepointProvider()
-except:
-    provider = DebugfsProvider()
+providers = []
+if options.tracepoints:
+    providers.append(TracepointProvider())
+if options.debugfs:
+    providers.append(DebugfsProvider())
+
+if len(providers) == 0:
+    try:
+        providers = [TracepointProvider()]
+    except:
+        providers = [DebugfsProvider()]
 
-stats = Stats(provider, fields = options.fields)
+stats = Stats(providers, fields = options.fields)
 
 if options.log:
     log(stats)