Messages in this thread | | | Date | Wed, 11 Feb 2009 14:39:55 -0600 | From | Jack Steiner <> | Subject | Re: [PATCH 0/8] git pull request for tip/tracing/core |
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On Wed, Feb 11, 2009 at 09:57:00AM -0800, Luck, Tony wrote: > > > Before we go and make the change, Peter brought up a good point on IRC. Is > > > there any reason that ia64 needs 1 << 14 IRQs? That's 16384! > > > > > > Perhaps the better solution wolud be (if possible), to simply lower the > > > number of bits. > > > > i'm the wrong person to be asked about that. (Cc:-ed the right people) > > People build some pretty big systems on ia64. SGI's largest has 4096 > cpus ... so 16384 IRQs is only 4 per cpu. That doesn't sound like very > many to me.
As long as per-cpu interrupts (ex., timer, cpe_hndlr, cmc_hndlr, etc) are not counted in the IRQ count, SGI is ok with 256 IRQs. We had problems overflowing the old limit of 256 but have worked around it.
If per-cpu interrupts ARE counted in the total IRQs, then we currently use 5 per-cpu interrupts for each cpu. A 4k cpu config will need 20k IRQs + additional IRQs for real devices.
I know the IRQ infrastructure has changed recently so this may no longer apply.
--- jack
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