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    SubjectRe: [PATCH] sparse_irq aka dyn_irq v13
    David Miller wrote:
    > From: Mike Travis <travis@sgi.com>
    > Date: Thu, 13 Nov 2008 16:15:12 -0800
    >
    >> David Miller wrote:
    >>> From: Mike Travis <travis@sgi.com>
    >>> Date: Thu, 13 Nov 2008 15:11:29 -0800
    >>>
    >>> We use a value of 256 and I've been booting linux on 128 cpu sparc64
    >>> systems with lots of PCI-E host controllers (and others have booted it
    >>> on even larger ones). All of which have several NUMA domains.
    >>>
    >>> It's not an issue.
    >> Are you saying that having a fixed count of IRQ's is not an issue? With
    >> NR_CPUS=4096 what would you fix it to? (Currently it's NR_CPUS * 32
    >> but that might not be sufficient.) Would NR_CPUS=16384 make it an issue?
    >
    > Nope, and nope. I frequently run kernels with NR_CPUS set to huge
    > values.
    >
    > It seems that the issue of x86 is that it has it's IRQ count tied to
    > the number of cpus, that's not very intelligent. Perhaps that part
    > should be rearranged somehow?

    Yes, you're probably right but it is what it is. Most of the irq vectors
    have more to do with cpus than with i/o devices (the system vectors, ipi,
    kdb and gru [a uv thing] interrupt vectors come first to mind.) These do
    by necessity need to grow with NR_CPUS, if you're fixing the total IRQ count.

    There's been a couple of different proposals to attempt to disassociate
    i/o and system vectors though even attempting to guess at the number of
    i/o devices is tricky. Every one of the 512 nodes on a UV system *may*
    have a number of i/o devices attached to them though practically this
    will be rare.


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