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Preemption mode selection is currently hardcoded on Kconfig choices. Introduce a dedicated option to tune preemption flavour at boot time, This will be only available on architectures efficiently supporting static calls in order not to tempt with the feature against additional overhead that might be prohibitive or undesirable. CONFIG_PREEMPT_DYNAMIC is automatically selected by CONFIG_PREEMPT if the architecture provides the necessary support (CONFIG_STATIC_CALL_INLINE, CONFIG_GENERIC_ENTRY, and provide with __preempt_schedule_function() / __preempt_schedule_notrace_function()). Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> [peterz: relax requirement to HAVE_STATIC_CALL] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20210118141223.123667-5-frederic@kernel.org
102 lines
3.7 KiB
Plaintext
102 lines
3.7 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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choice
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prompt "Preemption Model"
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default PREEMPT_NONE
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config PREEMPT_NONE
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bool "No Forced Preemption (Server)"
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help
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This is the traditional Linux preemption model, geared towards
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throughput. It will still provide good latencies most of the
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time, but there are no guarantees and occasional longer delays
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are possible.
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Select this option if you are building a kernel for a server or
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scientific/computation system, or if you want to maximize the
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raw processing power of the kernel, irrespective of scheduling
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latencies.
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config PREEMPT_VOLUNTARY
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bool "Voluntary Kernel Preemption (Desktop)"
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depends on !ARCH_NO_PREEMPT
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help
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This option reduces the latency of the kernel by adding more
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"explicit preemption points" to the kernel code. These new
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preemption points have been selected to reduce the maximum
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latency of rescheduling, providing faster application reactions,
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at the cost of slightly lower throughput.
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This allows reaction to interactive events by allowing a
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low priority process to voluntarily preempt itself even if it
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is in kernel mode executing a system call. This allows
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applications to run more 'smoothly' even when the system is
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under load.
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Select this if you are building a kernel for a desktop system.
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config PREEMPT
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bool "Preemptible Kernel (Low-Latency Desktop)"
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depends on !ARCH_NO_PREEMPT
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select PREEMPTION
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select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
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select PREEMPT_DYNAMIC if HAVE_PREEMPT_DYNAMIC
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help
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This option reduces the latency of the kernel by making
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all kernel code (that is not executing in a critical section)
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preemptible. This allows reaction to interactive events by
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permitting a low priority process to be preempted involuntarily
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even if it is in kernel mode executing a system call and would
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otherwise not be about to reach a natural preemption point.
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This allows applications to run more 'smoothly' even when the
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system is under load, at the cost of slightly lower throughput
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and a slight runtime overhead to kernel code.
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Select this if you are building a kernel for a desktop or
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embedded system with latency requirements in the milliseconds
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range.
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config PREEMPT_RT
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bool "Fully Preemptible Kernel (Real-Time)"
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depends on EXPERT && ARCH_SUPPORTS_RT
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select PREEMPTION
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help
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This option turns the kernel into a real-time kernel by replacing
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various locking primitives (spinlocks, rwlocks, etc.) with
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preemptible priority-inheritance aware variants, enforcing
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interrupt threading and introducing mechanisms to break up long
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non-preemptible sections. This makes the kernel, except for very
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low level and critical code paths (entry code, scheduler, low
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level interrupt handling) fully preemptible and brings most
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execution contexts under scheduler control.
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Select this if you are building a kernel for systems which
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require real-time guarantees.
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endchoice
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config PREEMPT_COUNT
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bool
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config PREEMPTION
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bool
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select PREEMPT_COUNT
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config PREEMPT_DYNAMIC
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bool
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help
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This option allows to define the preemption model on the kernel
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command line parameter and thus override the default preemption
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model defined during compile time.
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The feature is primarily interesting for Linux distributions which
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provide a pre-built kernel binary to reduce the number of kernel
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flavors they offer while still offering different usecases.
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The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
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but if runtime patching is not available for the specific architecture
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then the potential overhead should be considered.
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Interesting if you want the same pre-built kernel should be used for
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both Server and Desktop workloads.
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