Move RT check into its own method, and save value.

mininet/node.py

@@ -640,12 +640,8 @@ class CPULimitedHost( Host ):
         # still does better with larger period values.
         self.period_us = kwargs.get( 'period_us', 100000 )
         self.sched = sched
-        if self.sched == 'rt':
-            release = quietRun( 'uname -r' ).strip('\r\n')
-            output = quietRun( 'grep CONFIG_RT_GROUP_SCHED /boot/config-%s' % release )
-            if output == '# CONFIG_RT_GROUP_SCHED is not set\n':
-                error( '\n*** error: please enable RT_GROUP_SCHED in your kernel\n' )
-                exit( 1 )
+        if sched == 'rt':
+            self.checkRtGroupSched()
             self.rtprio = 20
 
     def cgroupSet( self, param, value, resource='cpu' ):
@@ -710,6 +706,19 @@ class CPULimitedHost( Host ):
         quota = int( self.period_us * f )
         return pstr, qstr, self.period_us, quota
 
+    _rtGroupSched = False   # internal class var: Is CONFIG_RT_GROUP_SCHED set?
+
+    @classmethod
+    def checkRtGroupSched( cls ):
+        "Check (Ubuntu,Debian) kernel config for CONFIG_RT_GROUP_SCHED for RT"
+        if not cls._rtGroupSched:
+            release = quietRun( 'uname -r' ).strip('\r\n')
+            output = quietRun( 'grep CONFIG_RT_GROUP_SCHED /boot/config-%s' % release )
+            if output == '# CONFIG_RT_GROUP_SCHED is not set\n':
+                error( '\n*** error: please enable RT_GROUP_SCHED in your kernel\n' )
+                exit( 1 )
+            cls._rtGroupSched = True
+
     def cfsInfo( self, f):
         "Internal method: return parameters for CFS bandwidth"
         pstr, qstr = 'cfs_period_us', 'cfs_quota_us'