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    SubjectRe: RCU question
    Manfred Spraul wrote:
    > George Anzinger wrote:
    >
    >>
    >> The "normal" idle loop just looks at the need_resched flag and goes
    >> right back to the hlt,
    >
    >
    > That's the problem: If a the tasklet does a wakeup then the reschedule
    > is delayed until the next interrupt.

    Not so. On the interrupt that runs the tasklet, on the way out via entry.S, the
    need_resched flag is checked and acted on. Thus the task switch is done prio to
    getting back to the hlt.

    > Testing need_resched and executing
    > hlt must be atomic, but it isn't - NMIs break the atomicity.

    Actually this is not required, especially if preemption is turned on.

    > Not a big deal, except if someone implements a tickless kernel.

    Well, it is not tickless, but VST that I am working on :). The notion is to
    turn off the ticks when in idle and there are not time events in the list.

    I think
    > we can ignore it for now [or was the thread started by someone who
    > want's to disable the hardware timer when the system is really idle?]

    Yep, me! But still, I keep a timer around to exit, it is just way more than a
    tick later (depending on what the next entry in the time list needs).
    >

    --
    George Anzinger george@mvista.com
    High-res-timers: http://sourceforge.net/projects/high-res-timers/

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