diff options
Diffstat (limited to 'init')
| -rw-r--r-- | init/Kconfig | 46 |
1 files changed, 27 insertions, 19 deletions
diff --git a/init/Kconfig b/init/Kconfig index 2d9b83104dc..be52daf4bc3 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -459,18 +459,10 @@ config TINY_RCU is not required. This option greatly reduces the memory footprint of RCU. -config TINY_PREEMPT_RCU - bool "Preemptible UP-only small-memory-footprint RCU" - depends on PREEMPT && !SMP - help - This option selects the RCU implementation that is designed - for real-time UP systems. This option greatly reduces the - memory footprint of RCU. - endchoice config PREEMPT_RCU - def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU ) + def_bool TREE_PREEMPT_RCU help This option enables preemptible-RCU code that is common between the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations. @@ -656,7 +648,7 @@ config RCU_BOOST_DELAY Accept the default if unsure. config RCU_NOCB_CPU - bool "Offload RCU callback processing from boot-selected CPUs (EXPERIMENTAL" + bool "Offload RCU callback processing from boot-selected CPUs" depends on TREE_RCU || TREE_PREEMPT_RCU default n help @@ -682,9 +674,10 @@ choice prompt "Build-forced no-CBs CPUs" default RCU_NOCB_CPU_NONE help - This option allows no-CBs CPUs to be specified at build time. - Additional no-CBs CPUs may be specified by the rcu_nocbs= - boot parameter. + This option allows no-CBs CPUs (whose RCU callbacks are invoked + from kthreads rather than from softirq context) to be specified + at build time. Additional no-CBs CPUs may be specified by + the rcu_nocbs= boot parameter. config RCU_NOCB_CPU_NONE bool "No build_forced no-CBs CPUs" @@ -692,25 +685,40 @@ config RCU_NOCB_CPU_NONE help This option does not force any of the CPUs to be no-CBs CPUs. Only CPUs designated by the rcu_nocbs= boot parameter will be - no-CBs CPUs. + no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU + kthreads whose names begin with "rcuo". All other CPUs will + invoke their own RCU callbacks in softirq context. + + Select this option if you want to choose no-CBs CPUs at + boot time, for example, to allow testing of different no-CBs + configurations without having to rebuild the kernel each time. config RCU_NOCB_CPU_ZERO bool "CPU 0 is a build_forced no-CBs CPU" depends on RCU_NOCB_CPU && !NO_HZ_FULL help - This option forces CPU 0 to be a no-CBs CPU. Additional CPUs - may be designated as no-CBs CPUs using the rcu_nocbs= boot - parameter will be no-CBs CPUs. + This option forces CPU 0 to be a no-CBs CPU, so that its RCU + callbacks are invoked by a per-CPU kthread whose name begins + with "rcuo". Additional CPUs may be designated as no-CBs + CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs. + All other CPUs will invoke their own RCU callbacks in softirq + context. Select this if CPU 0 needs to be a no-CBs CPU for real-time - or energy-efficiency reasons. + or energy-efficiency reasons, but the real reason it exists + is to ensure that randconfig testing covers mixed systems. config RCU_NOCB_CPU_ALL bool "All CPUs are build_forced no-CBs CPUs" depends on RCU_NOCB_CPU help This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs= - boot parameter will be ignored. + boot parameter will be ignored. All CPUs' RCU callbacks will + be executed in the context of per-CPU rcuo kthreads created for + this purpose. Assuming that the kthreads whose names start with + "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter + on the remaining CPUs, but might decrease memory locality during + RCU-callback invocation, thus potentially degrading throughput. Select this if all CPUs need to be no-CBs CPUs for real-time or energy-efficiency reasons. |