diff options
Diffstat (limited to 'kernel/Kconfig.preempt')
| -rw-r--r-- | kernel/Kconfig.preempt | 87 |
1 files changed, 60 insertions, 27 deletions
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index 4bb60418779f..f4602f8f35d4 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -1,14 +1,13 @@ - choice - prompt "Preemption Model" - default PREEMPT_NONE + prompt "Preemption Mode" + default PREEMPT_RT config PREEMPT_NONE bool "No Forced Preemption (Server)" help - This is the traditional Linux preemption model, geared towards + 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 + time but there are no guarantees and occasional long delays are possible. Select this option if you are building a kernel for a server or @@ -21,7 +20,7 @@ config PREEMPT_VOLUNTARY 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 + preemption points have been selected to minimize the maximum latency of rescheduling, providing faster application reactions, at the cost of slightly lower throughput. @@ -33,38 +32,73 @@ config PREEMPT_VOLUNTARY Select this if you are building a kernel for a desktop system. -config PREEMPT +config PREEMPT_DESKTOP 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) + 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. + otherwise not about to reach a preemption point. This allows + applications to run more 'smoothly' even when the system is + under load, at the cost of slighly lower throughput and a + slight runtime overhead to kernel code. + + (According to profiles, when this mode is selected then even + during kernel-intense workloads the system is in an immediately + preemptible state more than 50% of the time.) Select this if you are building a kernel for a desktop or embedded system with latency requirements in the milliseconds range. +config PREEMPT_RT + bool "Complete Preemption (Real-Time)" + select PREEMPT_SOFTIRQS + select PREEMPT_HARDIRQS + select PREEMPT_RCU + select RT_MUTEXES + help + This option further reduces the scheduling latency of the + kernel by replacing almost every spinlock used by the kernel + with preemptible mutexes and thus making all but the most + critical kernel code involuntarily preemptible. The remaining + handful of lowlevel non-preemptible codepaths are short and + have a deterministic latency of a couple of tens of + microseconds (depending on the hardware). This also allows + applications to run more 'smoothly' even when the system is + under load, at the cost of lower throughput and runtime + overhead to kernel code. + + (According to profiles, when this mode is selected then even + during kernel-intense workloads the system is in an immediately + preemptible state more than 95% of the time.) + + Select this if you are building a kernel for a desktop, + embedded or real-time system with guaranteed latency + requirements of 100 usecs or lower. + endchoice +config PREEMPT + bool + default y + depends on PREEMPT_DESKTOP || PREEMPT_RT + config PREEMPT_SOFTIRQS bool "Thread Softirqs" default n # depends on PREEMPT help This option reduces the latency of the kernel by 'threading' - soft interrupts. This means that all softirqs will execute - in softirqd's context. While this helps latency, it can also - reduce performance. + soft interrupts. This means that all softirqs will execute + in softirqd's context. While this helps latency, it can also + reduce performance. - The threading of softirqs can also be controlled via - /proc/sys/kernel/softirq_preemption runtime flag and the - sofirq-preempt=0/1 boot-time option. + The threading of softirqs can also be controlled via + /proc/sys/kernel/softirq_preemption runtime flag and the + sofirq-preempt=0/1 boot-time option. Say N if you are unsure. @@ -75,15 +109,14 @@ config PREEMPT_HARDIRQS select PREEMPT_SOFTIRQS help This option reduces the latency of the kernel by 'threading' - hardirqs. This means that all (or selected) hardirqs will run - in their own kernel thread context. While this helps latency, - this feature can also reduce performance. + hardirqs. This means that all (or selected) hardirqs will run + in their own kernel thread context. While this helps latency, + this feature can also reduce performance. - The threading of hardirqs can also be controlled via the - /proc/sys/kernel/hardirq_preemption runtime flag and the - hardirq-preempt=0/1 boot-time option. Per-irq threading can - be enabled/disable via the /proc/irq/<IRQ>/<handler>/threaded - runtime flags. + The threading of hardirqs can also be controlled via the + /proc/sys/kernel/hardirq_preemption runtime flag and the + hardirq-preempt=0/1 boot-time option. Per-irq threading can + be enabled/disable via the /proc/irq/<IRQ>/<handler>/threaded + runtime flags. Say N if you are unsure. - |