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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

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