[Haskell-cafe] Re: Joels Time Leak

Simon Marlow simonmar at microsoft.com
Thu Jan 5 07:40:27 EST 2006

Bulat Ziganshin wrote:
> Hello Simon,
> Wednesday, January 04, 2006, 7:33:22 PM, you wrote:
>>>>>The minimum time between context switches is 20 milliseconds.
>>>SM> Sure, there's no reason why we couldn't do this.  Of course, even
>>>SM> idle Haskell processes will be ticking away in the background, so
>>>SM> there's a reason not to make the interval too short.  What do  
>>>SM> you think is reasonable?
>>>Simon, the talk is about changing GHC _tick_, which is a _minimal_
>>>possible context switch interval
> SM> Yes, I know.
> in this case, why you say that idle processes will be ticking in
> background? it's entirely up to program writers/users if they wants to
> decrease this interval. by default switches will occur in the same 20
> ms, lesser tick will have no impact on ordinary programs as long as
> default switching time will be not changed

It will have an impact, because the tick signal has to be delivered to 
the process and the signal handler run.  The impact on CPU time is 
small, but could be noticeable if we were to choose too small an 
interval.  Furthermore, the ticker prevents idle Haskell processes from 
being completely swapped out (that problem already exists).


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