Messages in this thread | | | Date | Mon, 7 Aug 2006 10:55:37 -0700 | From | "Randy.Dunlap" <> | Subject | Re: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig |
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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) > --
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