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@xxxxxxxxxx>
---
I tested this on an arm64 juno target, to get that to boot I had to
backport the dtb from v4.0-rc6 to v3.18.11-rt6.
arch/arm64/Kconfig | 2 ++
arch/arm64/include/asm/thread_info.h | 3 +++
arch/arm64/kernel/asm-offsets.c | 1 +
arch/arm64/kernel/entry.S | 14 ++++++++++----
4 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9532f8d..62f4e00 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -59,7 +59,9 @@ 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_FORCED_THREADING
select IRQ_DOMAIN
select MODULES_USE_ELF_RELA
select NO_BOOTMEM
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 459bf8e..3e24ea1 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -50,6 +50,7 @@ struct thread_info {
struct exec_domain *exec_domain; /* execution domain */
struct restart_block restart_block;
int preempt_count; /* 0 => preemptable, <0 => bug */
+ int preempt_lazy_count; /* 0 => preemptable, <0 => bug */
int cpu; /* cpu */
};
@@ -108,6 +109,7 @@ static inline struct thread_info *current_thread_info(void)
#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
@@ -124,6 +126,7 @@ static inline struct thread_info *current_thread_info(void)
#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)
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 9a9fce0..f774136 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -36,6 +36,7 @@ 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_EXEC_DOMAIN, offsetof(struct thread_info, exec_domain));
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 726b910..8a631bb 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -347,11 +347,16 @@ el1_irq:
#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
+ tbz x0, #_TIF_NEED_RESCHED, 2f // needs rescheduling?
+
+ ldr w24, [tsk, #TI_PREEMPT_LAZY] // get preempt lazy count
+ cbnz w24, 1f // preempt 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
@@ -364,7 +369,8 @@ el1_preempt:
mov x24, lr
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, 2b // needs rescheduling?
+ tbnz x0, #_TIF_NEED_RESCHED_LAZY, 2b
ret x24
#endif
--
2.1.4
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
