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    SubjectRe: 2.6.16-rc6-mm2

    * Andi Kleen <ak@suse.de> wrote:

    > > below is an updated patch that includes fixups for i386 - but the real
    > > fix should be to properly reduce the per-arch local.h footprint to the
    > > bare minimum possible, and to do this fix on the asm-generic headers.
    >
    > I think an even better approach would be to use local_save_flags() /
    > local_restore_flags () and then use a normal increment and get rid of
    > smp_processor_id completely.

    local_irq_save()/local_irq_restore() you must have meant :-)

    > I've never seen any evidence that the complex and bloated code
    > generated by this is any better that just enabling/disabling
    > interrupts.
    >
    > In the x86 world P4 has costly cli/sti, but I wouldn't expect that
    > problem to be very widespread.

    i think you are right - but if someone goes the trouble of implementing
    per-arch support for local increments then i'm not against it. (except
    if the generated code is grossly inefficient) There are architectures
    where cli/sti hurts alot.

    In any case, on x86 we should switch to a cli/sti implementation indeed
    - it will quite likely have alot smaller footprint than __per_cpu_offset
    based approaches.

    Although on x86_64 we'd probably be pretty OK if all per-cpu variables
    were in the PDA and were thus at a constant %gs-relative offset. But for
    now we only have data_offset in the PDA so there's one more unnecessary
    indirection.

    Ingo
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