x86/entry: Convert reschedule interrupt to IDTENTRY_SYSVEC_SIMPLE

The scheduler IPI does not need the full interrupt entry handling logic
when the entry is from kernel mode. Use IDTENTRY_SYSVEC_SIMPLE and spare
all the overhead.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202119.835425642@linutronix.de

arch/x86/entry/entry_64.S

@@ -956,10 +956,6 @@ apicinterrupt3 \num \sym \do_sym
 POP_SECTION_IRQENTRY
 .endm
 
-#ifdef CONFIG_SMP
-apicinterrupt RESCHEDULE_VECTOR			reschedule_interrupt		smp_reschedule_interrupt
-#endif
-
 /*
  * Reload gs selector with exception handling
  * edi:  new selector

arch/x86/include/asm/entry_arch.h

@@ -10,6 +10,3 @@
  * is no hardware IRQ pin equivalent for them, they are triggered
  * through the ICC by us (IPIs)
  */
-#ifdef CONFIG_SMP
-BUILD_INTERRUPT(reschedule_interrupt,RESCHEDULE_VECTOR)
-#endif

arch/x86/include/asm/hw_irq.h

@@ -28,9 +28,6 @@
 #include <asm/irq.h>
 #include <asm/sections.h>
 
-/* Interrupt handlers registered during init_IRQ */
-extern asmlinkage void reschedule_interrupt(void);
-
 #ifdef	CONFIG_X86_LOCAL_APIC
 struct irq_data;
 struct pci_dev;

arch/x86/include/asm/idtentry.h

@@ -600,6 +600,7 @@ DECLARE_IDTENTRY_SYSVEC(X86_PLATFORM_IPI_VECTOR,	sysvec_x86_platform_ipi);
 #endif
 
 #ifdef CONFIG_SMP
+DECLARE_IDTENTRY(RESCHEDULE_VECTOR,			sysvec_reschedule_ipi);
 DECLARE_IDTENTRY_SYSVEC(IRQ_MOVE_CLEANUP_VECTOR,	sysvec_irq_move_cleanup);
 DECLARE_IDTENTRY_SYSVEC(REBOOT_VECTOR,			sysvec_reboot);
 DECLARE_IDTENTRY_SYSVEC(CALL_FUNCTION_SINGLE_VECTOR,	sysvec_call_function_single);

arch/x86/include/asm/trace/common.h

@@ -5,12 +5,8 @@
 DECLARE_STATIC_KEY_FALSE(trace_pagefault_key);
 #define trace_pagefault_enabled()			\
 	static_branch_unlikely(&trace_pagefault_key)
-DECLARE_STATIC_KEY_FALSE(trace_resched_ipi_key);
-#define trace_resched_ipi_enabled()			\
-	static_branch_unlikely(&trace_resched_ipi_key)
 #else
 static inline bool trace_pagefault_enabled(void) { return false; }
-static inline bool trace_resched_ipi_enabled(void) { return false; }
 #endif
 
 #endif

arch/x86/include/asm/trace/irq_vectors.h

@@ -10,9 +10,6 @@
 
 #ifdef CONFIG_X86_LOCAL_APIC
 
-extern int trace_resched_ipi_reg(void);
-extern void trace_resched_ipi_unreg(void);
-
 DECLARE_EVENT_CLASS(x86_irq_vector,
 
 	TP_PROTO(int vector),
@@ -37,18 +34,6 @@ DEFINE_EVENT_FN(x86_irq_vector, name##_exit,	\
 	TP_PROTO(int vector),			\
 	TP_ARGS(vector), NULL, NULL);
 
-#define DEFINE_RESCHED_IPI_EVENT(name)		\
-DEFINE_EVENT_FN(x86_irq_vector, name##_entry,	\
-	TP_PROTO(int vector),			\
-	TP_ARGS(vector),			\
-	trace_resched_ipi_reg,			\
-	trace_resched_ipi_unreg);		\
-DEFINE_EVENT_FN(x86_irq_vector, name##_exit,	\
-	TP_PROTO(int vector),			\
-	TP_ARGS(vector),			\
-	trace_resched_ipi_reg,			\
-	trace_resched_ipi_unreg);
-
 /*
  * local_timer - called when entering/exiting a local timer interrupt
  * vector handler
@@ -99,7 +84,7 @@ TRACE_EVENT_PERF_PERM(irq_work_exit, is_sampling_event(p_event) ? -EPERM : 0);
 /*
  * reschedule - called when entering/exiting a reschedule vector handler
  */
-DEFINE_RESCHED_IPI_EVENT(reschedule);
+DEFINE_IRQ_VECTOR_EVENT(reschedule);
 
 /*
  * call_function - called when entering/exiting a call function interrupt

arch/x86/kernel/idt.c

@@ -112,7 +112,7 @@ static const __initconst struct idt_data def_idts[] = {
  */
 static const __initconst struct idt_data apic_idts[] = {
 #ifdef CONFIG_SMP
-	INTG(RESCHEDULE_VECTOR,			reschedule_interrupt),
+	INTG(RESCHEDULE_VECTOR,			asm_sysvec_reschedule_ipi),
 	INTG(CALL_FUNCTION_VECTOR,		asm_sysvec_call_function),
 	INTG(CALL_FUNCTION_SINGLE_VECTOR,	asm_sysvec_call_function_single),
 	INTG(IRQ_MOVE_CLEANUP_VECTOR,		asm_sysvec_irq_move_cleanup),

arch/x86/kernel/smp.c

@@ -220,26 +220,15 @@ static void native_stop_other_cpus(int wait)
 
 /*
  * Reschedule call back. KVM uses this interrupt to force a cpu out of
- * guest mode
+ * guest mode.
  */
-__visible void __irq_entry smp_reschedule_interrupt(struct pt_regs *regs)
+DEFINE_IDTENTRY_SYSVEC_SIMPLE(sysvec_reschedule_ipi)
 {
 	ack_APIC_irq();
+	trace_reschedule_entry(RESCHEDULE_VECTOR);
 	inc_irq_stat(irq_resched_count);
-
-	if (trace_resched_ipi_enabled()) {
-		/*
-		 * scheduler_ipi() might call irq_enter() as well, but
-		 * nested calls are fine.
-		 */
-		irq_enter();
-		trace_reschedule_entry(RESCHEDULE_VECTOR);
-		scheduler_ipi();
-		trace_reschedule_exit(RESCHEDULE_VECTOR);
-		irq_exit();
-		return;
-	}
 	scheduler_ipi();
+	trace_reschedule_exit(RESCHEDULE_VECTOR);
 }
 
 DEFINE_IDTENTRY_SYSVEC(sysvec_call_function)

arch/x86/kernel/tracepoint.c

@@ -25,20 +25,3 @@ void trace_pagefault_unreg(void)
 {
 	static_branch_dec(&trace_pagefault_key);
 }
-
-#ifdef CONFIG_SMP
-
-DEFINE_STATIC_KEY_FALSE(trace_resched_ipi_key);
-
-int trace_resched_ipi_reg(void)
-{
-	static_branch_inc(&trace_resched_ipi_key);
-	return 0;
-}
-
-void trace_resched_ipi_unreg(void)
-{
-	static_branch_dec(&trace_resched_ipi_key);
-}
-
-#endif