Jamie Lokier wrote:
>
> yodaiken@fsmlabs.com wrote:
> > As far as I can tell,
> > only place need_resched is set is in the scheduler and the sched idle loop.
> > This is what makes Ingo's latency patch less dangerous: need_resched is hard
> > to set. Your scenario requires that an interrupt routine, interrupting
> > kernel mode, set needs_resched. Where does this happen?
>
> Whenever an interrupt wakes up a process. Alan says it's uncommon, but
> it depends what devices you're using. Some device drivers do it for all
> interrupts, if a process is waiting for some information from the device.
>
> -- Jamie
I don't know much about existing drivers. I know for embedded systems,
processes reading files and getting blocked, interrupt handlers (or its
bottom-half handler) waking them up is *VERY COMMON*.
I do agree that the window is small. (That is the reason I have to
patch kernel in order to deterministically create the scenario in my
test)
Unfortunately, for most embedded systems, 99.99% of times being correct
is not good enough.
Jun
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