Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | [PATCH] sched: Split preemption model selection between DYNAMIC & !DYNAMIC | Date | Tue, 9 Nov 2021 15:10:57 +0000 |
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From: Mike Galbraith <efault@gmx.de>
Commit c597bfddc9e9 ("sched: Provide Kconfig support for default dynamic preempt mode") changed the selectable config names for the preemption model. This means a config file must now select
CONFIG_PREEMPT_BEHAVIOUR=y
rather than
CONFIG_PREEMPT=y
to get a preemptible kernel. This means all arch config files would need to be updated - right now they'll all end up with the default CONFIG_PREEMPT_NONE_BEHAVIOUR.
Rather than touch a good hundred of config files, split the preemption model selection based on PREEMPT_DYNAMIC. !PREEMPT_DYNAMIC reverts to the old behaviour with CONFIG_PREEMPT & friends being the user-visible config, while PREEMPT_DYNAMIC exposes the _BEHAVIOUR counterparts.
Signed-off-by: Mike Galbraith <efault@gmx.de> [Changelog; deduplicated some config logic] Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> --- kernel/Kconfig.preempt | 80 +++++++++++++++++++++++------------------- 1 file changed, 43 insertions(+), 37 deletions(-)
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index 60f1bfc3c7b2..4e60afae248e 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -1,12 +1,32 @@ # SPDX-License-Identifier: GPL-2.0-only +config PREEMPT_DYNAMIC + bool "Preemption behaviour defined on boot" + depends on HAVE_PREEMPT_DYNAMIC && !ARCH_NO_PREEMPT + select PREEMPT + help + This option allows to define the preemption model on the kernel + command line parameter and thus override the default preemption + model defined during compile time. + + The feature is primarily interesting for Linux distributions which + provide a pre-built kernel binary to reduce the number of kernel + flavors they offer while still offering different usecases. + + The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled + but if runtime patching is not available for the specific architecture + then the potential overhead should be considered. + + Interesting if you want the same pre-built kernel should be used for + both Server and Desktop workloads. + choice prompt "Preemption Model" - default PREEMPT_NONE_BEHAVIOUR + default PREEMPT_NONE -config PREEMPT_NONE_BEHAVIOUR +config PREEMPT_NONE bool "No Forced Preemption (Server)" - select PREEMPT_NONE if !PREEMPT_DYNAMIC + depends on !PREEMPT_DYNAMIC help This is the traditional Linux preemption model, geared towards throughput. It will still provide good latencies most of the @@ -18,10 +38,9 @@ config PREEMPT_NONE_BEHAVIOUR raw processing power of the kernel, irrespective of scheduling latencies. -config PREEMPT_VOLUNTARY_BEHAVIOUR +config PREEMPT_VOLUNTARY bool "Voluntary Kernel Preemption (Desktop)" - depends on !ARCH_NO_PREEMPT - select PREEMPT_VOLUNTARY if !PREEMPT_DYNAMIC + depends on !ARCH_NO_PREEMPT && !PREEMPT_DYNAMIC help This option reduces the latency of the kernel by adding more "explicit preemption points" to the kernel code. These new @@ -37,10 +56,11 @@ config PREEMPT_VOLUNTARY_BEHAVIOUR Select this if you are building a kernel for a desktop system. -config PREEMPT_BEHAVIOUR +config PREEMPT bool "Preemptible Kernel (Low-Latency Desktop)" depends on !ARCH_NO_PREEMPT - select PREEMPT + select PREEMPTION + select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK help This option reduces the latency of the kernel by making all kernel code (that is not executing in a critical section) @@ -75,16 +95,23 @@ config PREEMPT_RT endchoice -config PREEMPT_NONE - bool +choice + prompt "Default boot-time Preemption Model" + depends on PREEMPT_DYNAMIC + default PREEMPT_NONE_BEHAVIOUR + help + This option defines the default preemption model of the kernel + if it hasn't been specified by the "preempt=" command line parameter. -config PREEMPT_VOLUNTARY - bool +config PREEMPT_NONE_BEHAVIOUR + bool "No Forced Preemption (Server)" -config PREEMPT - bool - select PREEMPTION - select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK +config PREEMPT_VOLUNTARY_BEHAVIOUR + bool "Voluntary Kernel Preemption (Desktop)" + +config PREEMPT_BEHAVIOUR + bool "Preemptible Kernel (Low-Latency Desktop)" +endchoice config PREEMPT_COUNT bool @@ -93,27 +120,6 @@ config PREEMPTION bool select PREEMPT_COUNT -config PREEMPT_DYNAMIC - bool "Preemption behaviour defined on boot" - depends on HAVE_PREEMPT_DYNAMIC - select PREEMPT - default y - help - This option allows to define the preemption model on the kernel - command line parameter and thus override the default preemption - model defined during compile time. - - The feature is primarily interesting for Linux distributions which - provide a pre-built kernel binary to reduce the number of kernel - flavors they offer while still offering different usecases. - - The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled - but if runtime patching is not available for the specific architecture - then the potential overhead should be considered. - - Interesting if you want the same pre-built kernel should be used for - both Server and Desktop workloads. - config SCHED_CORE bool "Core Scheduling for SMT" depends on SCHED_SMT -- 2.25.1
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