Commit 12d79baf authored by Ingo Molnar's avatar Ingo Molnar
Browse files

rcu: provide RCU options on non-preempt architectures too 



Impact: build fix

Some old architectures still do not use kernel/Kconfig.preempt, so the
moving of the RCU options there broke their build:

 In file included from /home/mingo/tip/include/linux/sem.h:81,
                 from /home/mingo/tip/include/linux/sched.h:69,
                 from /home/mingo/tip/arch/alpha/kernel/asm-offsets.c:9:
 /home/mingo/tip/include/linux/rcupdate.h:62:2: error: #error "Unknown RCU implementation specified to kernel configuration"

Move these options back to init/Kconfig, which every architecture
includes.

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 64db4cff

init/Kconfig

+74 −0
Original line number Diff line number Diff line
@@ -928,6 +928,80 @@ source "block/Kconfig" 
config PREEMPT_NOTIFIERS

	bool



choice

	prompt "RCU Implementation"

	default CLASSIC_RCU



config CLASSIC_RCU

	bool "Classic RCU"

	help

	  This option selects the classic RCU implementation that is

	  designed for best read-side performance on non-realtime

	  systems.



	  Select this option if you are unsure.



config TREE_RCU

	bool "Tree-based hierarchical RCU"

	help

	  This option selects the RCU implementation that is

	  designed for very large SMP system with hundreds or

	  thousands of CPUs.



config PREEMPT_RCU

	bool "Preemptible RCU"

	depends on PREEMPT

	help

	  This option reduces the latency of the kernel by making certain

	  RCU sections preemptible. Normally RCU code is non-preemptible, if

	  this option is selected then read-only RCU sections become

	  preemptible. This helps latency, but may expose bugs due to

	  now-naive assumptions about each RCU read-side critical section

	  remaining on a given CPU through its execution.



endchoice



config RCU_TRACE

	bool "Enable tracing for RCU"

	depends on TREE_RCU || PREEMPT_RCU

	help

	  This option provides tracing in RCU which presents stats

	  in debugfs for debugging RCU implementation.



	  Say Y here if you want to enable RCU tracing

	  Say N if you are unsure.



config RCU_FANOUT

	int "Tree-based hierarchical RCU fanout value"

	range 2 64 if 64BIT

	range 2 32 if !64BIT

	depends on TREE_RCU

	default 64 if 64BIT

	default 32 if !64BIT

	help

	  This option controls the fanout of hierarchical implementations

	  of RCU, allowing RCU to work efficiently on machines with

	  large numbers of CPUs.  This value must be at least the cube

	  root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit

	  systems and up to 262,144 for 64-bit systems.



	  Select a specific number if testing RCU itself.

	  Take the default if unsure.



config RCU_FANOUT_EXACT

	bool "Disable tree-based hierarchical RCU auto-balancing"

	depends on TREE_RCU

	default n

	help

	  This option forces use of the exact RCU_FANOUT value specified,

	  regardless of imbalances in the hierarchy.  This is useful for

	  testing RCU itself, and might one day be useful on systems with

	  strong NUMA behavior.



	  Without RCU_FANOUT_EXACT, the code will balance the hierarchy.



	  Say N if unsure.



config TREE_RCU_TRACE

	def_bool RCU_TRACE && TREE_RCU

	select DEBUG_FS

kernel/Kconfig.preempt

+0 −75
Original line number Diff line number Diff line
@@ -52,78 +52,3 @@ config PREEMPT 


endchoice

choice

	prompt "RCU Implementation"

	default CLASSIC_RCU



config CLASSIC_RCU

	bool "Classic RCU"

	help

	  This option selects the classic RCU implementation that is

	  designed for best read-side performance on non-realtime

	  systems.

	  

	  Select this option if you are unsure.



config TREE_RCU

	bool "Tree-based hierarchical RCU"

	help

	  This option selects the RCU implementation that is

	  designed for very large SMP system with hundreds or

	  thousands of CPUs.



config PREEMPT_RCU

	bool "Preemptible RCU"

	depends on PREEMPT

	help

	  This option reduces the latency of the kernel by making certain

	  RCU sections preemptible. Normally RCU code is non-preemptible, if

	  this option is selected then read-only RCU sections become

	  preemptible. This helps latency, but may expose bugs due to

	  now-naive assumptions about each RCU read-side critical section

	  remaining on a given CPU through its execution.



endchoice



config RCU_TRACE

	bool "Enable tracing for RCU"

	depends on TREE_RCU || PREEMPT_RCU

	help

	  This option provides tracing in RCU which presents stats

	  in debugfs for debugging RCU implementation.



	  Say Y here if you want to enable RCU tracing

	  Say N if you are unsure.



config RCU_FANOUT

	int "Tree-based hierarchical RCU fanout value"

	range 2 64 if 64BIT

	range 2 32 if !64BIT

	depends on TREE_RCU

	default 64 if 64BIT

	default 32 if !64BIT

	help

	  This option controls the fanout of hierarchical implementations

	  of RCU, allowing RCU to work efficiently on machines with

	  large numbers of CPUs.  This value must be at least the cube

	  root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit

	  systems and up to 262,144 for 64-bit systems.



	  Select a specific number if testing RCU itself.

	  Take the default if unsure.



config RCU_FANOUT_EXACT

	bool "Disable tree-based hierarchical RCU auto-balancing"

	depends on TREE_RCU

	default n

	help

	  This option forces use of the exact RCU_FANOUT value specified,

	  regardless of imbalances in the hierarchy.  This is useful for

	  testing RCU itself, and might one day be useful on systems with

	  strong NUMA behavior.



	  Without RCU_FANOUT_EXACT, the code will balance the hierarchy.



	  Say n if unsure.

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