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    SubjectRe: Faster timers for Linux 2.1.22

    On Mon, 27 Jan 1997, Theodore Y. Ts'o wrote:

    > From: Keith Owens <>
    > Date: Mon, 27 Jan 1997 12:01:00 +1100
    > As for 'buffering', after disable_bh is called, the next interrupt of
    > any kind including (AFAIK) the timer tick will run any outstanding
    > bottom half code. This takes precedence over user driven code. It's a
    > tradeoff, a more local lock and a slightly delayed bh against a global
    > lock that hits every piece of code.
    > Bottom half routines are run when the kernel is on its way out to
    > user-mode. [...]

    with one small exception if my understanding of entry.S is correct:

    #ifdef __SMP__
    cmpl $0,SYMBOL_NAME(intr_count)
    jne 1f
    9: movl SYMBOL_NAME(bh_mask),%eax
    andl SYMBOL_NAME(bh_active),%eax
    jne handle_bottom_half

    Thus 'slow irq handlers' (keyboard, some networking drivers) and the timer
    irq [they all take the ret_from_sys_call path] call 'do_bottom_half()'
    even if they interrupt kernel code.

    -- mingo

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