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

[Guo Ren]

On Tue, Feb 24, 2026 at 9:40 AM Guo Ren <guoren@xxxxxxxxxx> wrote:
>
> On Fri, Feb 20, 2026 at 5:28 PM Jisheng Zhang <jszhang@xxxxxxxxxx> wrote:
> >
> > 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%
> Thx for the work. It's a visible improvement.
>
> Compared to the original handler pointer approach, this solution
> introduces no observable drawbacks. Since the static_call alternative
> requires further analysis and consensus, adopting this implementation
> serves as a pragmatic interim step.
>
> So, I give:
> Reviewed-by: Guo Ren (Alibaba Damo Academy) <guoren@xxxxxxxxxx>

Oh, don't forget Mark's suggestion for the uninitialized handler,
which is also suitable for genirq:

"That means that if set_handle_irq() isn't called, an IRQ will result in
a call to that bogus address rather than default_handle_irq(), ..."

Maybe we need an empty _handle_arch_irq instance as a default for the
early stage.

>
> >
> > Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
> > ---
> >  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
> >
>
>
> --
> Best Regards
>  Guo Ren



-- 
Best Regards
 Guo Ren