Messages in this thread | | | Subject | RE: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig | Date | Mon, 7 Aug 2006 11:11:25 -0500 | From | "Protasevich, Natalie" <> |
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> > Currrently 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 Moores 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. > > > > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> > > --- > > arch/x86_64/Kconfig | 13 +++++++++++++ > > include/asm-x86_64/irq.h | 3 ++- > > 2 files changed, 15 insertions(+), 1 deletions(-) > > > > diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig index > > 7598d99..d744e5b 100644 > > --- a/arch/x86_64/Kconfig > > +++ b/arch/x86_64/Kconfig > > @@ -384,6 +384,19 @@ config NR_CPUS > > This is purely to save memory - each supported CPU requires > > memory in the static kernel configuration. > > > > +config NR_IRQS > > + int "Maximum number of IRQs (224-4096)" > > + range 256 4096 > > + depends on SMP > > + default "4096" > > + help > > + This allows you to specify the maximum number of IRQs > which this > > + kernel will support. Current maximum is 4096 IRQs as that > > + is slightly larger than has observed in the field. > > + > > + This is purely to save memory - each supported IRQ requires > > + memory in the static kernel configuration. > > If (a) "nor does hardware typically provide that many irq sources" > and (b) "This is purely to save memory", why is the default > 4096 instead of something smaller? >
4k being a humble maximum is definitely a relative term here, but on the system with "only" 64 or 128 processors the cpu*224 would be much higher :) However, maybe CONFIG_TINY that Andi suggested would leverage this number also. What do you think, Eric?
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