On Tue, Sep 28, 2010 at 04:51:48PM +0800, Huang Ying wrote:
> +++ b/arch/x86/kernel/irq_work.c
> @@ -0,0 +1,30 @@
> +/*
> + * x86 specific code for irq_work
> + *
> + * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra <pzijlstr@xxxxxxxxxx>
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/irq_work.h>
> +#include <linux/hardirq.h>
> +#include <asm/apic.h>
> +
> +void smp_irq_work_interrupt(struct pt_regs *regs)
> +{
> + irq_enter();
> + ack_APIC_irq();
> + inc_irq_stat(apic_irq_work_irqs);
> + irq_work_run();
> + irq_exit();
> +}
> +
> +void arch_irq_work_raise(void)
> +{
> +#ifdef CONFIG_X86_LOCAL_APIC
> + if (!cpu_has_apic)
> + return;
> +
> + apic->send_IPI_self(IRQ_WORK_VECTOR);
> + apic_wait_icr_idle();
> +#endif
> +}
So basically, CONFIG_X86_LOCAL_APIC == !HAVE_IRQ_WORK ?
But IIUC, this will fallback to the timer interrupt:
> @@ -1279,7 +1279,10 @@ void update_process_times(int user_tick)
> run_local_timers();
> rcu_check_callbacks(cpu, user_tick);
> printk_tick();
> - perf_event_do_pending();
> +#ifdef CONFIG_IRQ_WORK
> + if (in_irq())
> + irq_work_run();
> +#endif
> scheduler_tick();
> run_posix_cpu_timers(p);
> }
Then HAVE_IRQ_WORK just means that the arch supports self IPIs.
So, CONFIG_IRQ_WORK doesn't need to depend on HAVE_IRQ_WORK
because of the timer fallback. But archs that support self
IPIs should avoid the above fallback because it bloats
the timer interrupt.
Perhaps CONFIG_HAVE_IRQ_WORK should be CONFIG_HAVE_IRQ_WORK_SOURCE
or CONFIG_HAVE_IRQ_WORK_TRIGGER to better denote the capability.
And then:
config IRQ_WORK_TRIGGER
depends on HAVE_IRQ_WORK_TRIGGER && IRQ_WORK
default y
And that would define the right condition to build the fallback
in the timer interrupt.
Or I am completely misunderstanding something?
Thanks.
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