Re: [PATCHv2 3/5] kernel/irq: make irq_{enter,exit}() in handle_domain_irq() arch optional

From: Pingfan Liu
Date: Tue Sep 28 2021 - 23:15:31 EST

On Tue, Sep 28, 2021 at 09:55:00AM +0100, Mark Rutland wrote:
> On Fri, Sep 24, 2021 at 09:28:35PM +0800, Pingfan Liu wrote:
> > handle_domain_irq() contains two major parts:
> > -1. irq_enter()/irq_exit(), which serves as hooks for rcu and trace etc.
> > -2. irq mapping and dispatching
> >
> > After the introduction of irqentry_enter()/irqentry_exit() and arch
> > specific counterpart (e.g. arm64), roughly speaking, rcu_irq_enter() has
> > already been called. Hence here comes requirement to move
> > irq_enter/irq_exit out of handle_domain_irq(). And arches should handle
> > about irq_enter_rcu()/irq_exit_rcu() by themself.
> >
> > Since there is still arches, which does not adopt irqentry_enter(), let
> > irq_enter()/irq_exit() arch optional in handle_domain_irq().
> The patch below looks good to me, but the commit message is a little
> hard to follow. How about:
> When an IRQ is taken, some accounting needs to be performed to enter
> and exit IRQ context around the IRQ handler. Historically arch code
> would leave this to the irqchip or core IRQ code, but these days we
> want this to happen in exception entry code, and architectures such as
> arm64 do this.
> Currently handle_domain_irq() performs this entry/exit accounting, and
> if used on an architecture where the entry code also does this, the
> entry/exit accounting will be performed twice per IRQ. This is
> problematic as core RCU code such as rcu_is_cpu_rrupt_from_idle()
> depends on this happening once per IRQ, and will not detect quescent
> periods correctly, leading to stall warnings.
> As irqchip drivers which use handle_domain_irq() need to work on
> architectures with or without their own entry/exit accounting, this
> patch makes handle_domain_irq() conditionally perform the entry
> accounting depending on a new HAVE_ARCH_IRQENTRY Kconfig symbol that
> architectures can select if they perform this entry accounting
> themselves.
> For architectures which do not select the symbol. there should be no
> functional change as a result of this patch.
Thanks for your precious time to improve the log. It looks great, and I
will use it in V2. I will keep learning to improve my level of log.

> With that commit message:
> Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>