Subject: arm: Add support for lazy preemption
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed Oct 31 12:04:11 2012 +0100

From: Thomas Gleixner <tglx@linutronix.de>

Implement the arm pieces for lazy preempt.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>


---
 arch/arm/Kconfig                   |    1 +
 arch/arm/include/asm/thread_info.h |    6 +++++-
 arch/arm/kernel/asm-offsets.c      |    1 +
 arch/arm/kernel/entry-armv.S       |   19 ++++++++++++++++---
 arch/arm/kernel/signal.c           |    3 ++-
 5 files changed, 25 insertions(+), 5 deletions(-)
---
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -109,6 +109,7 @@ config ARM
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
+	select HAVE_PREEMPT_LAZY
 	select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -52,6 +52,7 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			preempt_lazy_count; /* 0 => preemptable, <0 => bug */
 	struct task_struct	*task;		/* main task structure */
 	__u32			cpu;		/* cpu */
 	__u32			cpu_domain;	/* cpu domain */
@@ -134,6 +135,7 @@ extern int vfp_restore_user_hwstate(stru
 #define TIF_SYSCALL_TRACEPOINT	6	/* syscall tracepoint instrumentation */
 #define TIF_SECCOMP		7	/* seccomp syscall filtering active */
 #define TIF_NOTIFY_SIGNAL	8	/* signal notifications exist */
+#define TIF_NEED_RESCHED_LAZY	9
 
 #define TIF_USING_IWMMXT	17
 #define TIF_MEMDIE		18	/* is terminating due to OOM killer */
@@ -148,6 +150,7 @@ extern int vfp_restore_user_hwstate(stru
 #define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
+#define _TIF_NEED_RESCHED_LAZY	(1 << TIF_NEED_RESCHED_LAZY)
 #define _TIF_USING_IWMMXT	(1 << TIF_USING_IWMMXT)
 
 /* Checks for any syscall work in entry-common.S */
@@ -157,7 +160,8 @@ extern int vfp_restore_user_hwstate(stru
 /*
  * Change these and you break ASM code in entry-common.S
  */
-#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_UPROBE | \
 				 _TIF_NOTIFY_SIGNAL)
 
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -43,6 +43,7 @@ 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_TASK,		offsetof(struct thread_info, task));
   DEFINE(TI_CPU,		offsetof(struct thread_info, cpu));
   DEFINE(TI_CPU_DOMAIN,		offsetof(struct thread_info, cpu_domain));
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -206,11 +206,18 @@ ENDPROC(__dabt_svc)
 
 #ifdef CONFIG_PREEMPTION
 	ldr	r8, [tsk, #TI_PREEMPT]		@ get preempt count
-	ldr	r0, [tsk, #TI_FLAGS]		@ get flags
 	teq	r8, #0				@ if preempt count != 0
+	bne	1f				@ return from exeption
+	ldr	r0, [tsk, #TI_FLAGS]		@ get flags
+	tst	r0, #_TIF_NEED_RESCHED		@ if NEED_RESCHED is set
+	blne	svc_preempt			@ preempt!
+
+	ldr	r8, [tsk, #TI_PREEMPT_LAZY]	@ get preempt lazy count
+	teq	r8, #0				@ if preempt lazy count != 0
 	movne	r0, #0				@ force flags to 0
-	tst	r0, #_TIF_NEED_RESCHED
+	tst	r0, #_TIF_NEED_RESCHED_LAZY
 	blne	svc_preempt
+1:
 #endif
 
 	svc_exit r5, irq = 1			@ return from exception
@@ -225,8 +232,14 @@ ENDPROC(__irq_svc)
 1:	bl	preempt_schedule_irq		@ irq en/disable is done inside
 	ldr	r0, [tsk, #TI_FLAGS]		@ get new tasks TI_FLAGS
 	tst	r0, #_TIF_NEED_RESCHED
+	bne	1b
+	tst	r0, #_TIF_NEED_RESCHED_LAZY
 	reteq	r8				@ go again
-	b	1b
+	ldr	r0, [tsk, #TI_PREEMPT_LAZY]	@ get preempt lazy count
+	teq	r0, #0				@ if preempt lazy count != 0
+	beq	1b
+	ret	r8				@ go again
+
 #endif
 
 __und_fault:
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -607,7 +607,8 @@ do_work_pending(struct pt_regs *regs, un
 	 */
 	trace_hardirqs_off();
 	do {
-		if (likely(thread_flags & _TIF_NEED_RESCHED)) {
+		if (likely(thread_flags & (_TIF_NEED_RESCHED |
+					   _TIF_NEED_RESCHED_LAZY))) {
 			schedule();
 		} else {
 			if (unlikely(!user_mode(regs)))