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    SubjectRe: [patch] rt: fix ipi kfree(), introduce IPI_SOFTIRQ

    * Ingo Molnar <mingo@elte.hu> wrote:

    > ------------------>
    > Subject: rt: fix ipi kfree(), introduce IPI_SOFTIRQ
    > From: Ingo Molnar <mingo@elte.hu>
    > Date: Thu Feb 12 09:06:11 CET 2009
    >
    > in 2.6.28 generic_smp_call_function_interrupt() grew a kfree(),
    > which is a rather complex, sleepable method under -rt. But the
    > IPI code runs as a hardirq - which cannot run such code.
    >
    > So defer this work to a softirq context instead. It still stays
    > on the same CPU so the percpu IPI assumptions are upheld.

    On a second thought ...

    I think we could eliminate the kfree() instead, and keep the
    atomicity of IPI cross-calls. Linus expressed doubts about
    the IPI kmalloc()/kfree() pair we do in the generic SMP IPI
    code, suggesting that it probably does not help performance
    all that much - so such a change might be upstream-able as well
    and would keep -rt closer to mainline.

    Ingo


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