[recipe.wrapper] Add option to reserve CPU core

Add functionality to wrapper to ask for an exclusive CPU core.

/reviewed-on nexedi/slapos!184

slapos/recipe/librecipe/generic.py

@@ -131,7 +131,7 @@ class GenericBaseRecipe(object):
 
   def createWrapper(self, name, command, parameters, comments=[],
       parameters_extra=False, environment=None,
-      pidfile=None
+      pidfile=None, reserve_cpu=False
   ):
     """
     Creates a shell script for process replacement.
@@ -139,6 +139,8 @@ class GenericBaseRecipe(object):
     Takes care of #! line limitation when the wrapped command is a script.
     if pidfile parameter is specified, then it will make the wrapper a singleton,
     accepting to run only if no other instance is running.
+
+    :param reserve_cpu: bool, try to reserve one core for the `command`
     """
 
     lines = [ '#!/bin/sh' ]
@@ -163,6 +165,14 @@ class GenericBaseRecipe(object):
           fi
           echo $$ > $pidfile""" % shlex.quote(pidfile)))
 
+    if reserve_cpu:
+      # if the CGROUPS cpuset is available (and prepared by slap format)
+      # request an exclusive CPU core for this process
+      lines.append(dedent("""
+        # put own PID into waiting list for exclusive CPU-core access
+        echo $$ >> ~/.slapos-cpu-exclusive
+        """))
+
     lines.append(dedent('''
     # If the wrapped command uses a shebang, execute the referenced
     # executable passing the script path as first argument.

slapos/recipe/wrapper.py

@@ -31,6 +31,16 @@ import os
 from slapos.recipe.librecipe import GenericBaseRecipe
 
 class Recipe(GenericBaseRecipe):
+    """Recipe to create a script from given command and options.
+
+    :param str command-line: shell command which launches the intended process
+    :param str wrapper-path: absolute path to file's destination
+
+    :param lines wait-for-files: list of files to wait for
+    :param str pidfile: path to pidfile ensure exclusivity for the process
+    :param bool parameters-extra: whether wrapper parameters are passed onto command
+    :param bool reserve-cpu: command will ask for an exclusive CPU core
+    """
     def install(self):
         command_line = shlex.split(self.options['command-line'])
         wrapper_path = self.options['wrapper-path']
@@ -38,6 +48,7 @@ class Recipe(GenericBaseRecipe):
         environment = self.options.get('environment')
         parameters_extra = self.options.get('parameters-extra')
         pidfile = self.options.get('pidfile')
+        reserve_cpu = self.options.get('reserve-cpu', False)
 
         if not wait_files and not environment:
           # Create a simple wrapper as shell script
@@ -47,6 +58,7 @@ class Recipe(GenericBaseRecipe):
              parameters=command_line[1:],
              parameters_extra=parameters_extra,
              pidfile=pidfile,
+             reserve_cpu=reserve_cpu
           )]
 
         # More complex needs: create a Python script as wrapper
@@ -76,5 +88,6 @@ class Recipe(GenericBaseRecipe):
              parameters=[],
              parameters_extra=parameters_extra,
              pidfile=pidfile,
+             reserve_cpu=reserve_cpu
         )]