[PATCH 2/3] genirq: use runtime constant to optimize handle_arch_irq access

[Jisheng Zhang <jszhang@kernel.org>]

Currently, on GENERIC_IRQ_MULTI_HANDLER platforms, the handle_arch_irq
is a pointer which is set during booting, and every irq processing needs
to access it, so it sits in hot code path. We can use the
runtime constant mechanism which was introduced by Linus to speed up
its accessing.

Tested on Sipeed Lichee Pi 4A (riscv64) board, the perf sched benchmark is
improved by ~5.8%

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 include/linux/irq.h | 4 +++-
 kernel/irq/handle.c | 8 +++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 951acbdb9f84..2ba4a8afb71e 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -1274,6 +1274,7 @@ void ipi_mux_process(void);
 int ipi_mux_create(unsigned int nr_ipi, void (*mux_send)(unsigned int cpu));
 
 #ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
+#include <asm/runtime-const.h>
 /*
  * Registers a generic IRQ handling function as the top-level IRQ handler in
  * the system, which is generally the first C code called from an assembly
@@ -1288,7 +1289,8 @@ int __init set_handle_irq(void (*handle_irq)(struct pt_regs *));
  * Allows interrupt handlers to find the irqchip that's been registered as the
  * top-level IRQ handler.
  */
-extern void (*handle_arch_irq)(struct pt_regs *) __ro_after_init;
+extern void (*_handle_arch_irq)(struct pt_regs *) __ro_after_init;
+#define handle_arch_irq runtime_const_ptr(_handle_arch_irq)
 asmlinkage void generic_handle_arch_irq(struct pt_regs *regs);
 #else
 #ifndef set_handle_irq
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index b7d52821837b..aac9e7b1301e 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -15,13 +15,14 @@
 #include <linux/kernel_stat.h>
 
 #include <asm/irq_regs.h>
+#include <asm/runtime-const.h>
 
 #include <trace/events/irq.h>
 
 #include "internals.h"
 
 #ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
-void (*handle_arch_irq)(struct pt_regs *) __ro_after_init;
+void (*_handle_arch_irq)(struct pt_regs *) __ro_after_init;
 #endif
 
 /**
@@ -270,10 +271,11 @@ irqreturn_t handle_irq_event(struct irq_desc *desc)
 #ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
 int __init set_handle_irq(void (*handle_irq)(struct pt_regs *))
 {
-	if (handle_arch_irq)
+	if (_handle_arch_irq)
 		return -EBUSY;
 
-	handle_arch_irq = handle_irq;
+	_handle_arch_irq = handle_irq;
+	runtime_const_init(ptr, _handle_arch_irq);
 	return 0;
 }
 
-- 
2.51.0