rcu: Add callback-free CPUs
RCU callback execution can add significant OS jitter and also can degrade
scheduling latency. This commit therefore adds the ability for selected
CPUs ("rcu_nocbs=" boot parameter) to have their callbacks offloaded to
kthreads. If the "rcu_nocb_poll" boot parameter is also specified, these
kthreads will do polling, removing the need for the offloaded CPUs to do
wakeups. At least one CPU must be doing normal callback processing:
currently CPU 0 cannot be selected as a no-CBs CPU. In addition, attempts
to offline the last normal-CBs CPU will fail.
This feature was inspired by Jim Houston's and Joe Korty's JRCU.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
6 files changed
