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SubjectRe: Overscheduling DOES happen with high web server load.
Greg Lindahl writes:
> > > Ok, you are right. The real problem is we are calculating goodness
> > > O(A*B).
> > >
> > > A= Number of processes on the runqueue
> > > B= Number of times schedule is called
> >
> > Don't underestimate the cost of searching the run queue. Put 10
> > processes on the run queue and you more than double the cost of
> > schedule() to another process. For 90+ tasks on the run queue, the
> > cost is dominated by the linear search.
> You are violently agreeing with Phil. The linear cost of searching the
> run queue is represented by A in his expression. That was the point of
> my little hack, which was to always take the first schedulable process
> in the queue, merely to see if that made life much better. And it
> seems to.

Maybe I didn't express myself clearly. I thought his (or someone's)
point was the cost of goodness() calculations dominated, the
implication being that reducing the cost of goodness() would speed
things up a lot. While true, the cost of scanning the task structures
is also high. But in essence, I agree with Phil.

Someone else suggested that the cost was in all those context
switches, which I dispute. Switching state is relatively cheap. And
this was my point (and as you say, Phil's too).



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