THE FOLD / GLITCH / RACE CONDITION / THE TIME SLICE
THE TIME SLICE
the half that decided the real value was never a number
1 WHAT IT IS · WHAT IT DOES · FACT OR FICTION
A short time slice makes the machine feel responsive and spends most of its day switching. A long one is efficient and makes everything feel stuck. The good value is in the middle and it is not a matter of taste.
LIT verified live. 50 jobs, a switch costing 2. At a quantum of 1 the machine spends 66.67% of all elapsed time switching, and mean turnaround is 3,871.1. At 128 the overhead is small and turnaround is worse again. The best of the eight measured is a quantum of 32, and it is an interior point — neither end of the range wins.
LIT verified live. 50 jobs, a switch costing 2. At a quantum of 1 the machine spends 66.67% of all elapsed time switching, and mean turnaround is 3,871.1. At 128 the overhead is small and turnaround is worse again. The best of the eight measured is a quantum of 32, and it is an interior point — neither end of the range wins.
2 HOW IT WAS WEAVED · AI + HUMAN
Every real scheduler tunes this, and the interior optimum is why: the two costs pull in opposite directions and neither can be minimised alone.
AVAN (AI) swept the quantum rather than arguing for a value, because the shape is the finding. 66.67% overhead at quantum 1 means two thirds of the machine’s life is bookkeeping — and the fix is not a faster switch, it is a longer turn.
AVAN (AI) swept the quantum rather than arguing for a value, because the shape is the finding. 66.67% overhead at quantum 1 means two thirds of the machine’s life is bookkeeping — and the fix is not a faster switch, it is a longer turn.
3 ONE DIMENSION
Quantum against turnaround and overhead.
4 TWO DIMENSIONS · INTERACTIVE
Set the quantum and the switch cost.
5 THREE DIMENSIONS + AVAN’S INVERSE
The green forward object: a turn, cut into pieces.
AVAN’s addition (the inverse-companion): the forward reading is that the quantum trades responsiveness against overhead. The inverse is that responsiveness is not a property of the machine at all. Turnaround, overhead, throughput — all of them are measured here. Whether 32 feels better than 8 is a fact about a person waiting, and no sweep on this page contains it. Read backwards, the interior optimum is the honest half of the problem, and the half that decided the value in the machine you are reading this on was never a number.
LIT 50 jobs with a switch costing 2 spend 66.67% of all elapsed time switching at a quantum of 1, for a mean turnaround of 3,871.1, while a quantum of 128 has small overhead and worse turnaround again - the best of the eight measured is 32, an interior point, so neither end of the range wins
FIG Every real scheduler tunes this, and the interior optimum is why: the two costs pull in opposite directions and neither can be minimised alone. AVAN swept the quantum rather than arguing for a value, because the shape is the finding. 66.67% overhead at quantum 1 means two thirds of the machine's life is bookkeeping - and the fix is not a faster switch, it is a longer turn.
FIG Every real scheduler tunes this, and the interior optimum is why: the two costs pull in opposite directions and neither can be minimised alone. AVAN swept the quantum rather than arguing for a value, because the shape is the finding. 66.67% overhead at quantum 1 means two thirds of the machine's life is bookkeeping - and the fix is not a faster switch, it is a longer turn.
◆ sealed .dlw.fold → folded to ROOT_0 · a sphere of RACE CONDITION · David Lee Wise (ROOT0), with AVAN