From: Peter Zijlstra <peterz@infradead.org> Date: Mon, 7 Oct 2024 09:46:12 +0200 Subject: [PATCH 3/5] sched: Enable PREEMPT_DYNAMIC for PREEMPT_RT In order to enable PREEMPT_DYNAMIC for PREEMPT_RT, remove PREEMPT_RT from the 'Preemption Model' choice. Strictly speaking PREEMPT_RT is not a change in how preemption works, but rather it makes a ton more code preemptible. Notably, take away NONE and VOLATILE options for PREEMPT_RT, they make no sense (but are techincally possible). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20241007075055.441622332@infradead.org Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/Kconfig.preempt | 12 +++++++----- kernel/sched/core.c | 2 ++ kernel/sched/debug.c | 4 ++-- 3 files changed, 11 insertions(+), 7 deletions(-) @ kernel/Kconfig.preempt:23 @ choice config PREEMPT_NONE bool "No Forced Preemption (Server)" + depends on !PREEMPT_RT select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC help This is the traditional Linux preemption model, geared towards @ kernel/Kconfig.preempt:39 @ config PREEMPT_NONE config PREEMPT_VOLUNTARY bool "Voluntary Kernel Preemption (Desktop)" depends on !ARCH_NO_PREEMPT + depends on !PREEMPT_RT select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC help This option reduces the latency of the kernel by adding more @ kernel/Kconfig.preempt:59 @ config PREEMPT_VOLUNTARY config PREEMPT bool "Preemptible Kernel (Low-Latency Desktop)" depends on !ARCH_NO_PREEMPT - select PREEMPT_BUILD + select PREEMPT_BUILD if !PREEMPT_DYNAMIC help This option reduces the latency of the kernel by making all kernel code (that is not executing in a critical section) @ kernel/Kconfig.preempt:79 @ config PREEMPT_LAZY bool "Scheduler controlled preemption model" depends on !ARCH_NO_PREEMPT depends on ARCH_HAS_PREEMPT_LAZY - select PREEMPT_BUILD + select PREEMPT_BUILD if !PREEMPT_DYNAMIC help This option provides a scheduler driven preemption model that is fundamentally similar to full preemption, but is less @ kernel/Kconfig.preempt:87 @ config PREEMPT_LAZY reduce lock holder preemption and recover some of the performance gains seen from using Voluntary preemption. +endchoice + config PREEMPT_RT bool "Fully Preemptible Kernel (Real-Time)" depends on EXPERT && ARCH_SUPPORTS_RT @ kernel/Kconfig.preempt:106 @ config PREEMPT_RT Select this if you are building a kernel for systems which require real-time guarantees. -endchoice - config PREEMPT_COUNT bool @ kernel/Kconfig.preempt:115 @ config PREEMPTION config PREEMPT_DYNAMIC bool "Preemption behaviour defined on boot" - depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT + depends on HAVE_PREEMPT_DYNAMIC select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY select PREEMPT_BUILD default y if HAVE_PREEMPT_DYNAMIC_CALL --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @ kernel/Kconfig.preempt:7409 @ int preempt_dynamic_mode = preempt_dynam int sched_dynamic_mode(const char *str) { +#ifndef CONFIG_PREEMPT_RT if (!strcmp(str, "none")) return preempt_dynamic_none; if (!strcmp(str, "voluntary")) return preempt_dynamic_voluntary; +#endif if (!strcmp(str, "full")) return preempt_dynamic_full; --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @ kernel/Kconfig.preempt:251 @ static int sched_dynamic_show(struct seq "none", "voluntary", "full", "lazy", }; int j = ARRAY_SIZE(preempt_modes) - !IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY); - int i; + int i = IS_ENABLED(CONFIG_PREEMPT_RT) * 2; - for (i = 0; i < j; i++) { + for (; i < j; i++) { if (preempt_dynamic_mode == i) seq_puts(m, "("); seq_puts(m, preempt_modes[i]);