bitbake: cooker/server: Fix up 100% CPU usage at idle

The recent inotify changes are causing a 100% cpu usage issue in the
idle handlers. To avoid this, we update the idle functions to optionally
report a float value which is the delay before the function needs to be
called again. 1 second is fine for the inotify handler, in reality its
more like 0.1s due to the default idle function sleep.

This reverts performance regressions of 1.5 minutes on a kernel build
and ~5-6 minutes on a image from scratch.

(Bitbake rev: 0e0ba408c2dce14a0fabd3fdf61d8465a031495b)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/xmlrpc.py

@@ -242,6 +242,9 @@ class XMLRPCServer(SimpleXMLRPCServer, BaseImplServer):
                         del self._idlefuns[function]
                     elif retval is True:
                         nextsleep = 0
+                    elif isinstance(retval, float):
+                        if (retval < nextsleep):
+                            nextsleep = retval
                     else:
                         fds = fds + retval
                 except SystemExit: