[net-next-2.6.git] / kernel / Kconfig.preempt


choice
	prompt "Preemption Model"
	default PREEMPT_NONE

config PREEMPT_NONE
	bool "No Forced Preemption (Server)"
	help
	  This is the traditional Linux preemption model, geared towards
	  throughput. It will still provide good latencies most of the
	  time, but there are no guarantees and occasional longer delays
	  are possible.

	  Select this option if you are building a kernel for a server or
	  scientific/computation system, or if you want to maximize the
	  raw processing power of the kernel, irrespective of scheduling
	  latencies.

config PREEMPT_VOLUNTARY
	bool "Voluntary Kernel Preemption (Desktop)"
	help
	  This option reduces the latency of the kernel by adding more
	  "explicit preemption points" to the kernel code. These new
	  preemption points have been selected to reduce the maximum
	  latency of rescheduling, providing faster application reactions,
	  at the cost of slightly lower throughput.

	  This allows reaction to interactive events by allowing a
	  low priority process to voluntarily preempt itself even if it
	  is in kernel mode executing a system call. This allows
	  applications to run more 'smoothly' even when the system is
	  under load.

	  Select this if you are building a kernel for a desktop system.

config PREEMPT
	bool "Preemptible Kernel (Low-Latency Desktop)"
	help
	  This option reduces the latency of the kernel by making
	  all kernel code (that is not executing in a critical section)
	  preemptible.  This allows reaction to interactive events by
	  permitting a low priority process to be preempted involuntarily
	  even if it is in kernel mode executing a system call and would
	  otherwise not be about to reach a natural preemption point.
	  This allows applications to run more 'smoothly' even when the
	  system is under load, at the cost of slightly lower throughput
	  and a slight runtime overhead to kernel code.

	  Select this if you are building a kernel for a desktop or
	  embedded system with latency requirements in the milliseconds
	  range.

endchoice

config PREEMPT_RCU
	bool "Preemptible RCU"
	depends on PREEMPT
	default n
	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.

	  Say N if you are unsure.

config RCU_TRACE
	bool "Enable tracing for RCU - currently stats in debugfs"
	depends on PREEMPT_RCU
	select DEBUG_FS
	default y
	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.
Commit	Line	Data
cc19ca86	1
f8cbd99b IM	2	choice
	3	prompt "Preemption Model"
	4	default PREEMPT_NONE
	5
	6	config PREEMPT_NONE
	7	bool "No Forced Preemption (Server)"
	8	help
	9	This is the traditional Linux preemption model, geared towards
	10	throughput. It will still provide good latencies most of the
	11	time, but there are no guarantees and occasional longer delays
	12	are possible.
	13
	14	Select this option if you are building a kernel for a server or
	15	scientific/computation system, or if you want to maximize the
	16	raw processing power of the kernel, irrespective of scheduling
	17	latencies.
	18
	19	config PREEMPT_VOLUNTARY
	20	bool "Voluntary Kernel Preemption (Desktop)"
cc19ca86	21	help
f8cbd99b IM	22	This option reduces the latency of the kernel by adding more
	23	"explicit preemption points" to the kernel code. These new
	24	preemption points have been selected to reduce the maximum
	25	latency of rescheduling, providing faster application reactions,
3dde6ad8	26	at the cost of slightly lower throughput.
f8cbd99b IM	27
	28	This allows reaction to interactive events by allowing a
	29	low priority process to voluntarily preempt itself even if it
	30	is in kernel mode executing a system call. This allows
	31	applications to run more 'smoothly' even when the system is
cc19ca86 IM	32	under load.
cc19ca86 IM	33
f8cbd99b IM	34	Select this if you are building a kernel for a desktop system.
	35
	36	config PREEMPT
	37	bool "Preemptible Kernel (Low-Latency Desktop)"
	38	help
	39	This option reduces the latency of the kernel by making
	40	all kernel code (that is not executing in a critical section)
	41	preemptible. This allows reaction to interactive events by
	42	permitting a low priority process to be preempted involuntarily
	43	even if it is in kernel mode executing a system call and would
	44	otherwise not be about to reach a natural preemption point.
	45	This allows applications to run more 'smoothly' even when the
3dde6ad8	46	system is under load, at the cost of slightly lower throughput
f8cbd99b IM	47	and a slight runtime overhead to kernel code.
	48
	49	Select this if you are building a kernel for a desktop or
	50	embedded system with latency requirements in the milliseconds
	51	range.
	52
	53	endchoice
cc19ca86	54
21bbb39c PM	55	config PREEMPT_RCU
	56	bool "Preemptible RCU"
	57	depends on PREEMPT
	58	default n
	59	help
	60	This option reduces the latency of the kernel by making certain
	61	RCU sections preemptible. Normally RCU code is non-preemptible, if
	62	this option is selected then read-only RCU sections become
	63	preemptible. This helps latency, but may expose bugs due to
	64	now-naive assumptions about each RCU read-side critical section
	65	remaining on a given CPU through its execution.
	66
	67	Say N if you are unsure.
	68
e260be67 PM	69	config RCU_TRACE
e260be67 PM	70	bool "Enable tracing for RCU - currently stats in debugfs"
21bbb39c	71	depends on PREEMPT_RCU
e260be67 PM	72	select DEBUG_FS
	73	default y
	74	help
	75	This option provides tracing in RCU which presents stats
	76	in debugfs for debugging RCU implementation.
	77
	78	Say Y here if you want to enable RCU tracing
	79	Say N if you are unsure.