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    SubjectRe: [RFC 00/13] smp: reduce stack requirements for genapic send_IPI_mask functions
    Ingo Molnar wrote:
    > * Mike Travis <travis@sgi.com> wrote:
    >
    >> [Note: all these changes require some more testing but I wanted to
    >> solicit comments before then, hence the "RFC" in the subject line.
    >> -thanks! Mike]
    >
    > these changes are certainly looking very nice.
    >
    > They do interact with a ton of high-flux topics in -tip, so i'd prefer
    > to start integrating/testing this straight away (today-ish), before the
    > target moves yet again. Are there any showstoppers that speak against
    > that?
    >
    > The plan would be to not keep this in a single topic but to spread them
    > into their closest topic (tip/x86/x2apic, tip/irq/sparseirq etc.) - are
    > there any cross-topic dependencies to be careful about? Most of the
    > commits seem to be standalone. The debug patch would go into
    > tip/cpus4096.
    >
    > And more generally: how far away are we from being able to introduce
    > struct cpumask and hide its implementation from most .c files? That
    > would be rather efficient in preventing it from being put on the stack
    > spuriously in one of the 30+ thousand Linux kernel source code files.
    > Just like we hide the true structure of things like 'struct kmem_cache'
    > and force them to always be used as pointers.
    >
    > Ingo

    What I'll do is resubmit the changes that have nothing to do with
    cpumask_ptr's first as they are mostly just "cleaning up extraneous
    temp cpumask variables". Then I'll try the redefine of cpumask_t to
    see what kind of hornet's nest is opened up.

    What do you think of a pool of temp cpumask_t's? That way, they
    could be made available early (before kmalloc is available). An
    atomic op could be used for reservation which when the zero-based
    percpu variables finally get completed, become very low cost.

    Thanks,
    Mike


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