| From: Anders Roxell <anders.roxell@linaro.org> |
| Date: Thu, 14 May 2015 17:52:17 +0200 |
| Subject: arch/arm64: Add lazy preempt support |
| |
| 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> |
| --- |
| 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 |
| @@ -76,6 +76,7 @@ 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 IOMMU_DMA if IOMMU_SUPPORT |
| select IRQ_DOMAIN |
| --- a/arch/arm64/include/asm/thread_info.h |
| +++ b/arch/arm64/include/asm/thread_info.h |
| @@ -49,6 +49,7 @@ 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 */ |
| }; |
| |
| @@ -103,6 +104,7 @@ 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 |
| @@ -118,6 +120,7 @@ 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 |
| @@ -363,11 +363,16 @@ 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 |
| @@ -381,6 +386,7 @@ 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 |
| |
| @@ -625,6 +631,7 @@ ENDPROC(cpu_switch_to) |
| */ |
| 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' |