🚀 go-pugleaf

In article <tonyn-0109950144230001@tonyn.tiac.net>, tonyn@tiac.net says...
>
>I see some discussion here about "negligable preemtion / interrupt overhead".
>
>On any CPU, interrupt processing requires a context switch (also required
>for preemption and system services).  In the old days, this required
>simply the amount of time the CPU required to start the interrupt (and
>finish it later) plus the instructions in the interrupt handler.
>
>Nowadays the penalty for an interrupt is much greater, because of
>processor caches (or rather, fast processors but memory at the same speed
>as before).  The context switch now requires flushing the cache, so the
>processor will run slowly for a while as instructions are fetched from
>"real memory".  Not only will this slow down interrupt processing
>(relative to the estimate from the number of instructions involved), it is
>unpredictable.  I estimate that processors are spending the same amount of
>real time servicing interrupts as the did years ago, but I may be wrong --
>it may take much longer now, due to cache flush and reload.
>
>Deterministic real-time processing is difficult to do with interrupts. 
>You really can't tell when all the interrupts will stack up at the same
>time, causing the lowest priority interrupt to wait a long time.  Coupled
>with the overhead of context switching, this makes interrupt-driven
>programming impractical for device controllers (such as, say, a car or a
>wheelchair).  Polling with a heartbeat timer is used instead.  The most
>time-critical tasks are polled oftenest.  Processing of different tasks is
>distributed in time by spreading out the polling.  Such systems can more
>easily be proved to work, which is comforting for the person in the
>wheelchair who is crossing a busy street.
>____________________________________________________________________
>TonyN.:'                                              tonyn@tiac.net
>      '

Who the hell do you think is going to understand this bullshit?  Geez, dude, 
you should get a part on star trek.  You do excellent techo-babble.