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    SubjectRe: [patch] Re: setitimer lowlatency-2.2.13-A1 questions
    Andrea Arcangeli wrote:
    > >
    > >Is there a special reason why do_bottom_half() calls __sti() and __cli()
    > >directly? This seems wrong, what about using the normal
    > >__save_flags()/__sti()/__restore_flags()?
    > The irq handler case by design doesn't need it. You must enter there with
    > irq disabled and you must exit with irq disabled (so you must enabled
    > and disable by hand before and after running the bhs).
    > For the ret to userspace case it could decrease a bit the bh latency but
    > it seems not a big issue, as right now a ret from syscall will act like
    > while returning from an irq after the bottom half path.
    I know that it's safe:
    * "real interrupts" need it.
    * schedule() calls "spin_lock_irq()" immediately after returning from
    * interrupts are cleared during IRET.

    But nevertheless I think that it's ugly that a function sometimes (even
    worse: rarely) disables interrupts: What if a cpu doesn't reenable
    interrupts during return to user space? do_bottom_half() is not
    architecture specific.


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