On Tue, Apr 30, 2013 at 02:46:12PM -0400, Dave Jones wrote: > On Tue, Apr 30, 2013 at 03:21:26PM +0000, Linux Kernel wrote: > > > +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. > > + > > +config RCU_NOCB_CPU_NONE > > + bool "No build_forced no-CBs CPUs" > > + depends on RCU_NOCB_CPU > > + 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. > > + > > +config RCU_NOCB_CPU_ZERO > > + bool "CPU 0 is a build_forced no-CBs CPU" > > + depends on RCU_NOCB_CPU > > + 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. > > + > > + Select this if CPU 0 needs to be a no-CBs CPU for real-time > > + or energy-efficiency reasons. > > + > > +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. > > + > > + Select this if all CPUs need to be no-CBs CPUs for real-time > > + or energy-efficiency reasons. > > Note that entering '?' when prompted in oldconfig only outputs the help > parameter from the choice section. I must defer to the Kconfig experts on this issue. I have added them on CC. > Additionally, nowhere in any of this text does it say what a "no-CB CPU" is, > or why I would care, or even what the downsides are for each option. In the absence of any Kconfig change, would the following be more helpful? +choice + prompt "Build-forced no-CBs CPUs" + default RCU_NOCB_CPU_NONE + help + 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" + depends on RCU_NOCB_CPU + 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, whose RCU callbacks will be invoked by per-CPU + rcuo kthreads. All other CPUs will invoke their own RCU + callbacks in softirq context. + +config RCU_NOCB_CPU_ZERO + bool "CPU 0 is a build_forced no-CBs CPU" + depends on RCU_NOCB_CPU + help + This option forces CPU 0 to be a no-CBs CPU, so that its + RCU callbacks are invoked by a per-CPU rcuo kthread. + 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. + +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. All CPUs' RCU callbacks will + be executed in the context of per-CPU rcuo kthreads created + for this purpose. + + Select this if all CPUs need to be no-CBs CPUs for real-time + or energy-efficiency reasons. > I nominate this changeset for an award for most obtuse kconfig text in 3.10 (so far) Woo-hoo!!! An award! ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
