Subject: arch/arm64: Add lazy preempt support From: Anders Roxell <anders.roxell@linaro.org> Date: Thu May 14 17:52:17 2015 +0200 From: Anders Roxell <anders.roxell@linaro.org> arm64 is missing support for PREEMPT_RT. The main feature which is lacking is support for lazy preemption. The arch-specific entry code, thread information structure definitions, and associated data tables have to be extended to provide this support. Then the Kconfig file has to be extended to indicate the support is available, and also to indicate that support for full RT preemption is now available. Signed-off-by: Anders Roxell <anders.roxell@linaro.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/preempt.h | 25 ++++++++++++++++++++++++- arch/arm64/include/asm/thread_info.h | 8 +++++++- arch/arm64/kernel/asm-offsets.c | 1 + arch/arm64/kernel/signal.c | 2 +- 5 files changed, 34 insertions(+), 3 deletions(-) --- Index: linux-6.3.0-rt11/arch/arm64/Kconfig =================================================================== @ linux-6.3.0-rt11/arch/arm64/Kconfig:210 @ config ARM64 select HAVE_PERF_USER_STACK_DUMP select HAVE_PREEMPT_DYNAMIC_KEY select HAVE_REGS_AND_STACK_ACCESS_API + select HAVE_PREEMPT_LAZY select HAVE_POSIX_CPU_TIMERS_TASK_WORK select HAVE_FUNCTION_ARG_ACCESS_API select MMU_GATHER_RCU_TABLE_FREE Index: linux-6.3.0-rt11/arch/arm64/include/asm/preempt.h =================================================================== --- linux-6.3.0-rt11.orig/arch/arm64/include/asm/preempt.h +++ linux-6.3.0-rt11/arch/arm64/include/asm/preempt.h @ linux-6.3.0-rt11/arch/arm64/Kconfig:74 @ static inline bool __preempt_count_dec_a * interrupt occurring between the non-atomic READ_ONCE/WRITE_ONCE * pair. */ - return !pc || !READ_ONCE(ti->preempt_count); + if (!pc || !READ_ONCE(ti->preempt_count)) + return true; +#ifdef CONFIG_PREEMPT_LAZY + if ((pc & ~PREEMPT_NEED_RESCHED)) + return false; + if (current_thread_info()->preempt_lazy_count) + return false; + return test_thread_flag(TIF_NEED_RESCHED_LAZY); +#else + return false; +#endif } static inline bool should_resched(int preempt_offset) { +#ifdef CONFIG_PREEMPT_LAZY + u64 pc = READ_ONCE(current_thread_info()->preempt_count); + if (pc == preempt_offset) + return true; + + if ((pc & ~PREEMPT_NEED_RESCHED) != preempt_offset) + return false; + + if (current_thread_info()->preempt_lazy_count) + return false; + return test_thread_flag(TIF_NEED_RESCHED_LAZY); +#else u64 pc = READ_ONCE(current_thread_info()->preempt_count); return pc == preempt_offset; +#endif } #ifdef CONFIG_PREEMPTION Index: linux-6.3.0-rt11/arch/arm64/include/asm/thread_info.h =================================================================== --- linux-6.3.0-rt11.orig/arch/arm64/include/asm/thread_info.h +++ linux-6.3.0-rt11/arch/arm64/include/asm/thread_info.h @ linux-6.3.0-rt11/arch/arm64/Kconfig:29 @ struct thread_info { #ifdef CONFIG_ARM64_SW_TTBR0_PAN u64 ttbr0; /* saved TTBR0_EL1 */ #endif + int preempt_lazy_count; /* 0 => preemptable, <0 => bug */ union { u64 preempt_count; /* 0 => preemptible, <0 => bug */ struct { @ linux-6.3.0-rt11/arch/arm64/Kconfig:72 @ int arch_dup_task_struct(struct task_str #define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */ #define TIF_MTE_ASYNC_FAULT 5 /* MTE Asynchronous Tag Check Fault */ #define TIF_NOTIFY_SIGNAL 6 /* signal notifications exist */ +#define TIF_NEED_RESCHED_LAZY 7 #define TIF_SYSCALL_TRACE 8 /* syscall trace active */ #define TIF_SYSCALL_AUDIT 9 /* syscall auditing */ #define TIF_SYSCALL_TRACEPOINT 10 /* syscall tracepoint for ftrace */ @ linux-6.3.0-rt11/arch/arm64/Kconfig:105 @ int arch_dup_task_struct(struct task_str #define _TIF_SVE (1 << TIF_SVE) #define _TIF_MTE_ASYNC_FAULT (1 << TIF_MTE_ASYNC_FAULT) #define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL) +#define _TIF_NEED_RESCHED_LAZY (1 << TIF_NEED_RESCHED_LAZY) -#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \ +#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY | \ + _TIF_SIGPENDING | \ _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \ _TIF_UPROBE | _TIF_MTE_ASYNC_FAULT | \ _TIF_NOTIFY_SIGNAL) @ linux-6.3.0-rt11/arch/arm64/Kconfig:117 @ int arch_dup_task_struct(struct task_str _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \ _TIF_SYSCALL_EMU) +#define _TIF_NEED_RESCHED_MASK (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY) + #ifdef CONFIG_SHADOW_CALL_STACK #define INIT_SCS \ .scs_base = init_shadow_call_stack, \ Index: linux-6.3.0-rt11/arch/arm64/kernel/asm-offsets.c =================================================================== --- linux-6.3.0-rt11.orig/arch/arm64/kernel/asm-offsets.c +++ linux-6.3.0-rt11/arch/arm64/kernel/asm-offsets.c @ linux-6.3.0-rt11/arch/arm64/Kconfig:36 @ int main(void) DEFINE(TSK_TI_CPU, offsetof(struct task_struct, thread_info.cpu)); DEFINE(TSK_TI_FLAGS, offsetof(struct task_struct, thread_info.flags)); DEFINE(TSK_TI_PREEMPT, offsetof(struct task_struct, thread_info.preempt_count)); + DEFINE(TSK_TI_PREEMPT_LAZY, offsetof(struct task_struct, thread_info.preempt_lazy_count)); #ifdef CONFIG_ARM64_SW_TTBR0_PAN DEFINE(TSK_TI_TTBR0, offsetof(struct task_struct, thread_info.ttbr0)); #endif Index: linux-6.3.0-rt11/arch/arm64/kernel/signal.c =================================================================== --- linux-6.3.0-rt11.orig/arch/arm64/kernel/signal.c +++ linux-6.3.0-rt11/arch/arm64/kernel/signal.c @ linux-6.3.0-rt11/arch/arm64/Kconfig:1281 @ static void do_signal(struct pt_regs *re void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags) { do { - if (thread_flags & _TIF_NEED_RESCHED) { + if (thread_flags & _TIF_NEED_RESCHED_MASK) { /* Unmask Debug and SError for the next task */ local_daif_restore(DAIF_PROCCTX_NOIRQ);