From: Anders Roxell Date: Thu, 14 May 2015 17:52:17 +0200 Subject: arch/arm64: Add lazy preempt support Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.1/patches-4.1.3-rt3.tar.xz 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 --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/thread_info.h | 3 +++ arch/arm64/kernel/asm-offsets.c | 1 + arch/arm64/kernel/entry.S | 13 ++++++++++--- 4 files changed, 15 insertions(+), 3 deletions(-) --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -69,6 +69,7 @@ config ARM64 select HAVE_PERF_REGS select HAVE_PERF_USER_STACK_DUMP select HAVE_RCU_TABLE_FREE + select HAVE_PREEMPT_LAZY select HAVE_SYSCALL_TRACEPOINTS select IRQ_DOMAIN select IRQ_FORCED_THREADING --- a/arch/arm64/include/asm/thread_info.h +++ b/arch/arm64/include/asm/thread_info.h @@ -47,6 +47,7 @@ struct thread_info { mm_segment_t addr_limit; /* address limit */ struct task_struct *task; /* main task structure */ int preempt_count; /* 0 => preemptable, <0 => bug */ + int preempt_lazy_count; /* 0 => preemptable, <0 => bug */ int cpu; /* cpu */ }; @@ -101,6 +102,7 @@ static inline struct thread_info *curren #define TIF_NEED_RESCHED 1 #define TIF_NOTIFY_RESUME 2 /* callback before returning to user */ #define TIF_FOREIGN_FPSTATE 3 /* CPU's FP state is not current's */ +#define TIF_NEED_RESCHED_LAZY 4 #define TIF_NOHZ 7 #define TIF_SYSCALL_TRACE 8 #define TIF_SYSCALL_AUDIT 9 @@ -117,6 +119,7 @@ static inline struct thread_info *curren #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED) #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) #define _TIF_FOREIGN_FPSTATE (1 << TIF_FOREIGN_FPSTATE) +#define _TIF_NEED_RESCHED_LAZY (1 << TIF_NEED_RESCHED_LAZY) #define _TIF_NOHZ (1 << TIF_NOHZ) #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE) #define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT) --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -35,6 +35,7 @@ int main(void) BLANK(); DEFINE(TI_FLAGS, offsetof(struct thread_info, flags)); DEFINE(TI_PREEMPT, offsetof(struct thread_info, preempt_count)); + DEFINE(TI_PREEMPT_LAZY, offsetof(struct thread_info, preempt_lazy_count)); DEFINE(TI_ADDR_LIMIT, offsetof(struct thread_info, addr_limit)); DEFINE(TI_TASK, offsetof(struct thread_info, task)); DEFINE(TI_CPU, offsetof(struct thread_info, cpu)); --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -367,11 +367,16 @@ ENDPROC(el1_sync) #ifdef CONFIG_PREEMPT get_thread_info tsk ldr w24, [tsk, #TI_PREEMPT] // get preempt count - cbnz w24, 1f // preempt count != 0 + cbnz w24, 2f // preempt count != 0 ldr x0, [tsk, #TI_FLAGS] // get flags - tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling? - bl el1_preempt + tbnz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling? + + ldr w24, [tsk, #TI_PREEMPT_LAZY] // get preempt lazy count + cbnz w24, 2f // preempt lazy count != 0 + tbz x0, #TIF_NEED_RESCHED_LAZY, 2f // needs rescheduling? 1: + bl el1_preempt +2: #endif #ifdef CONFIG_TRACE_IRQFLAGS bl trace_hardirqs_on @@ -385,6 +390,7 @@ ENDPROC(el1_irq) 1: bl preempt_schedule_irq // irq en/disable is done inside ldr x0, [tsk, #TI_FLAGS] // get new tasks TI_FLAGS tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling? + tbnz x0, #TIF_NEED_RESCHED_LAZY, 1b // needs rescheduling? ret x24 #endif @@ -622,6 +628,7 @@ ENDPROC(cpu_switch_to) str x0, [sp, #S_X0] // returned x0 work_pending: tbnz x1, #TIF_NEED_RESCHED, work_resched + tbnz x1, #TIF_NEED_RESCHED_LAZY, work_resched /* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */ ldr x2, [sp, #S_PSTATE] mov x0, sp // 'regs'