Re: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig

Randy.Dunlap
2006-08-07T17:52:56Z

On Mon, 07 Aug 2006 11:30:24 -0600 Eric W. Biederman wrote:

> Currently on a SMP system we can theoretically support
> NR_CPUS*224 irqs. Unfortunately our data structures
> don't cope will with that many irqs, nor does hardware
> typically provide that many irq sources.
>
> With the number of cores starting to follow Moore's Law,
> and the apicid limits being raised beyond an 8bit
> number trying to track our current maximum with our
> current data structures would be fatal and wasteful.
>
> So this patch decouples the number of irqs we support
> from the number of cpus. We can revisit this decision
> once someone reworks the current data structures.
>
> This version has my stupid typos fix and the true maximum
> exposed to make it clear that I have a low default. The
> worst that I can see happening is there won't be any
> per_cpu space left for modules if someone sets this
> too high, but the system should still boot.
>
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> ---
>
> This of course applies to the -mm tree because the rest
> of the irq work is not yet in the mainline kernel.
>
> arch/x86_64/Kconfig | 14 ++++++++++++++
> include/asm-x86_64/irq.h | 3 ++-
> 2 files changed, 16 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig
> index 7598d99..cea78d7 100644
> --- a/arch/x86_64/Kconfig
> +++ b/arch/x86_64/Kconfig
> @@ -384,6 +384,20 @@ config NR_CPUS
> This is purely to save memory - each supported CPU requires
> memory in the static kernel configuration.

Thanks for the language fixes.
I'm confused about one thing. What is NR_IRQS for non-SMP?
Does it default to 4096 or something else?

Does this build on non-SMP? Is CONFIG_NR_IRQS defined for non-SMP?

> +config NR_IRQS
> + int "Maximum number of IRQs (224-57344)"
> + range 224 57344
> + depends on SMP
> + default "4096"
> + help
> + This allows you to specify the maximum number of IRQs which this
> + kernel will support. Current default is 4096 IRQs as that
> + is slightly larger than has observed in the field. Setting
> + a noticeably larger value will exhaust your per cpu memory,
> + and waste memory in the per irq arrays.
> +
> + If unsure leave this at 4096.
> +
> config HOTPLUG_CPU
> bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
> depends on SMP && HOTPLUG && EXPERIMENTAL
> diff --git a/include/asm-x86_64/irq.h b/include/asm-x86_64/irq.h
> index 5006c6e..34b264a 100644
> --- a/include/asm-x86_64/irq.h
> +++ b/include/asm-x86_64/irq.h
> @@ -31,7 +31,8 @@ #define NR_VECTORS 256
>
> #define FIRST_SYSTEM_VECTOR 0xef /* duplicated in hw_irq.h */
>
> -#define NR_IRQS (NR_VECTORS + (32 *NR_CPUS))
> +/* We can use at most NR_CPUS*224 irqs at one time */
> +#define NR_IRQS (CONFIG_NR_IRQS)
> #define NR_IRQ_VECTORS NR_IRQS
>
> static __inline__ int irq_canonicalize(int irq)
> --

---
~Randy