Another Derivation X X ֒ − → XY X Y X ֒ − → ε Y ֒ − → YY X Y Y Y Y ֒ − → X Y ֒ − → ε X Y Y X ⇒ XY ⇒ XYY ⇒ XYYY ⇒ XYY ⇒ XY ⇒ X ⇒ XY ⇒ XX Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Another Derivation X X ֒ − → XY X Y X ֒ − → ε Y ֒ − → YY X Y Y Y Y ֒ − → X Y ֒ − → ε X Y Y X ⇒ XY ⇒ XYY ⇒ XYYY ⇒ XYY ⇒ XY ⇒ X ⇒ XY ⇒ XX ⇒ X Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Another Derivation X X ֒ − → XY X Y X ֒ − → ε Y ֒ − → YY X Y Y Y Y ֒ − → X Y ֒ − → ε X Y Y X ⇒ XY ⇒ XYY ⇒ XYYY ⇒ XYY ⇒ XY ⇒ X ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Another Derivation X X ֒ − → XY X Y X ֒ − → ε Y ֒ − → YY X Y Y Y Y ֒ − → X Y ֒ − → ε X Y Y X ⇒ XY ⇒ XYY ⇒ XYYY ⇒ XYY ⇒ XY ⇒ X ⇒ XY ⇒ XX ⇒ X ⇒ ε Time: 10 (number of nodes) Space: 4 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Another Derivation X X ֒ − → XY X Y X ֒ − → ε Y ֒ − → YY X Y Y Y Y ֒ − → X Y ֒ − → ε X Y Y X ⇒ XY ⇒ XYY ⇒ XYYY XYYY ⇒ XYY ⇒ XY ⇒ X ⇒ XY ⇒ XX ⇒ X ⇒ ε Time: 10 (number of nodes) Space: 4 4 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Another Derivation X X ֒ − → XY X Y X ֒ − → ε Y ֒ − → YY Each finite tree has its X Y Y Y Probability (does not depend on scheduler) Y ֒ − → X Time (does not depend on scheduler) Y ֒ − → ε X Y Y Space (depends on scheduler) X ⇒ XY ⇒ XYY ⇒ XYYY XYYY ⇒ XYY ⇒ XY ⇒ X ⇒ XY ⇒ XX ⇒ X ⇒ ε Time: 10 (number of nodes) Space: 4 4 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Another Derivation X X ֒ − → XY X Y X ֒ − → ε Y ֒ − → YY Each finite tree has its X Y Y Y Probability (does not depend on scheduler) Y ֒ − → X Time (does not depend on scheduler) Y ֒ − → ε X Y Y Space (depends on scheduler) Raises questions like: What is the expected time and the expected space? X ⇒ XY ⇒ XYY ⇒ XYYY XYYY ⇒ XYY ⇒ XY ⇒ X ⇒ XY ⇒ XX ⇒ X ⇒ ε How are these random variables distributed? Time: 10 (number of nodes) Space: 4 4 Time has been studied before. We focus on space. Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Related Work: Branching Processes X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X Y Y Y ֒ 0 . 1 Y − → X ֒ 0 . 6 X Y Y Y − → ε ֒ Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Related Work: Branching Processes X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X Y Y Y ֒ 0 . 1 Y − → X ֒ 0 . 6 X Y Y Y − → ε ֒ Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Related Work: Branching Processes X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X Y Y Y ֒ 0 . 1 Y − → X ֒ 0 . 6 X Y Y Y − → ε ֒ Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Related Work: Branching Processes X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X Y Y Y ֒ 0 . 1 Y − → X ֒ 0 . 6 X Y Y Y − → ε ֒ Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Related Work: Branching Processes X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X Y Y Y ֒ 0 . 1 Y − → X ֒ 0 . 6 X Y Y Y − → ε ֒ Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Related Work: Branching Processes X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X Y Y Y ֒ 0 . 1 Y − → X ֒ 0 . 6 X Y Y Y − → ε ֒ Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Related Work: Branching Processes X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X Y Y Y ֒ 0 . 1 Y − → X ֒ 0 . 6 X Y Y Y − → ε ֒ Branching Processes have been extensively studied. They are models for biological or physical systems. But they assume an unbounded number of “processors”. Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Termination Probability X 0 . 2 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 2 0 . 3 0 . 3 Y − → YY X Y Y Y ֒ 0 . 1 0 . 8 0 . 1 0 . 6 0 . 3 Y − → X ֒ 0 . 6 X Y Y Y − → ε ֒ 0 . 8 0 . 6 0 . 6 Each tree has its probability. The sum of these probabilities is the “termination probability”. Is it always 1? Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Termination Probability and the function f A task system induces a vector f ( x ) . � x � f x ( x , y ) � � For our example: x = and f ( x ) = with y f y ( x , y ) 0 . 2 � X − → XY ֒ f x ( x , y ) = 0 . 2 xy + 0 . 8 0 . 8 X − → ε ֒ 0 . 3 − → YY Y ֒ f y ( x , y ) = 0 . 3 y 2 + 0 . 1 x + 0 . 6 0 . 1 − → X Y ֒ 0 . 6 Y − → ε ֒ Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Termination Probability and the function f A task system induces a vector f ( x ) . � x � f x ( x , y ) � � For our example: x = and f ( x ) = with y f y ( x , y ) 0 . 2 � X − → XY ֒ f x ( x , y ) = 0 . 2 xy + 0 . 8 0 . 8 X − → ε ֒ 0 . 3 − → YY Y ֒ f y ( x , y ) = 0 . 3 y 2 + 0 . 1 x + 0 . 6 0 . 1 − → X Y ֒ 0 . 6 Y − → ε ֒ Proposition (well-known, see [Harris]) The termination probability is the (first component of the) least fixed point of f . Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
The function f � termination probability = 1 The subcritical case: expected time = finite 1 . 2 0 . 4 X − → XX ֒ 1 0 . 6 f ( x ) = 0 . 4 x 2 + 0 . 6 X − → ε ֒ 0 . 8 0 . 6 0 . 4 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
The function f � termination probability < 1 The supercritical case: expected time = ∞ 1 . 2 0 . 7 X − → XX ֒ 1 0 . 3 X − → ε ֒ f ( x ) = 0 . 7 x 2 + 0 . 3 0 . 8 0 . 6 0 . 4 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
The function f � termination probability = 1 The critical case: expected time = ∞ 1 . 2 0 . 5 X − → XX ֒ 1 0 . 5 X − → ε ֒ f ( x ) = 0 . 5 x 2 + 0 . 5 0 . 8 0 . 6 0 . 4 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
The function f � termination probability = 1 The critical case: expected time = ∞ 1 . 2 0 . 5 X − → XX ֒ 1 0 . 5 X − → ε ֒ f ( x ) = 0 . 5 x 2 + 0 . 5 0 . 8 0 . 6 Assumption 0 . 4 We assume termination probability = 1 in the following, i.e., subcritical or critical. 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling Given a tree t with two children t 0 , t 1 . What is the optimal scheduling? t t 0 t 1 S op ( t 0 ) + 1 , S op ( t 1 ) � � max , S op ( t ) = S op ( t 1 ) + 1 , S op ( t 0 ) � � max Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling Given a tree t with two children t 0 , t 1 . What is the optimal scheduling? t t 0 t 1 � S op ( t 0 ) + 1 , S op ( t 1 ) � max , S op ( t ) = S op ( t 1 ) + 1 , S op ( t 0 ) � � max Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling Given a tree t with two children t 0 , t 1 . What is the optimal scheduling? t t 0 t 1 � S op ( t 0 ) + 1 , S op ( t 1 ) � max , S op ( t ) = S op ( t 1 ) + 1 , S op ( t 0 ) � � max Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling Given a tree t with two children t 0 , t 1 . What is the optimal scheduling? t t 0 t 1 � S op ( t 0 ) + 1 , S op ( t 1 ) � max , S op ( t ) = S op ( t 1 ) + 1 , S op ( t 0 ) � � max Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling Given a tree t with two children t 0 , t 1 . What is the optimal scheduling? t t 0 t 1 � S op ( t 0 ) + 1 , S op ( t 1 ) � max , S op ( t ) = S op ( t 1 ) + 1 , S op ( t 0 ) � � max Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling Given a tree t with two children t 0 , t 1 . What is the optimal scheduling? t t 0 t 1 � S op ( t 0 ) + 1 , S op ( t 1 ) � max , S op ( t ) = min S op ( t 1 ) + 1 , S op ( t 0 ) � � max Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling Given a tree t with just one child t 0 . What is the optimal scheduling? t t 0 S op ( t ) = Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling Given a tree t with just one child t 0 . What is the optimal scheduling? t t 0 S op ( t ) = S op ( t 0 ) Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling So we can determine S op for any tree t : � � max { S op ( t 0 ) + 1 , S op ( t 1 ) } , min if t has two children t 0 , t 1 max { S op ( t 1 ) + 1 , S op ( t 0 ) } S op ( t ) = S op ( t 0 ) if t has one child t 0 1 if t has no children. Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Optimal Scheduling So we can determine S op for any tree t : � � max { S op ( t 0 ) + 1 , S op ( t 1 ) } , min if t has two children t 0 , t 1 max { S op ( t 1 ) + 1 , S op ( t 0 ) } S op ( t ) = S op ( t 0 ) if t has one child t 0 1 if t has no children. What is the distribution of S op , if trees are randomly generated? Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Newton’s Method Let g ( x ) := f ( x ) − x and apply Newton’s method to g ( x ) = 0: 1 . 2 1 f ( x ) = 0 . 4 x 2 + 0 . 6 0 . 8 0 . 6 0 . 4 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Newton’s Method Let g ( x ) := f ( x ) − x and apply Newton’s method to g ( x ) = 0: 1 . 2 1 0 . 8 0 . 6 g ( x ) = f ( x ) − x 0 . 4 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Newton’s Method Let g ( x ) := f ( x ) − x and apply Newton’s method to g ( x ) = 0: 1 . 2 1 0 . 8 0 . 6 g ( x ) = f ( x ) − x 0 . 4 0 . 2 ν ( 0 ) 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Newton’s Method Let g ( x ) := f ( x ) − x and apply Newton’s method to g ( x ) = 0: 1 . 2 1 0 . 8 0 . 6 g ( x ) = f ( x ) − x 0 . 4 0 . 2 ν ( 0 ) ν ( 1 ) 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Newton’s Method Let g ( x ) := f ( x ) − x and apply Newton’s method to g ( x ) = 0: 1 . 2 1 0 . 8 0 . 6 g ( x ) = f ( x ) − x 0 . 4 0 . 2 ν ( 2 ) ν ( 0 ) ν ( 1 ) 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Newton’s Method Let g ( x ) := f ( x ) − x and apply Newton’s method to g ( x ) = 0: 1 . 2 Proposition (Etessami,Yannakakis, 2005) 1 Newton’s method converges to the least solution. 0 . 8 0 . 6 g ( x ) = f ( x ) − x 0 . 4 0 . 2 ν ( 2 ) ν ( 0 ) ν ( 1 ) 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Newton’s Method Let g ( x ) := f ( x ) − x and apply Newton’s method to g ( x ) = 0: 1 . 2 Proposition (Etessami,Yannakakis, 2005) 1 Newton’s method converges to the least solution. 0 . 8 The least solution is = 1. Why is he talking about Newton’s method?? 0 . 6 g ( x ) = f ( x ) − x 0 . 4 0 . 2 ν ( 2 ) ν ( 0 ) ν ( 1 ) 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Newton’s Method Let g ( x ) := f ( x ) − x and apply Newton’s method to g ( x ) = 0: 1 . 2 Proposition (Etessami,Yannakakis, 2005) 1 Newton’s method converges to the least solution. 0 . 8 The least solution is = 1. Why is he talking about Newton’s method?? 0 . 6 g ( x ) = f ( x ) − x 0 . 4 Theorem � � S op ≤ k = ν ( k ) Pr 0 . 2 ν ( 2 ) ν ( 0 ) ν ( 1 ) 0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Tail Bounds for the Optimal Scheduler Theorem � S op ≤ k � = ν ( k ) Pr It follows: � � S op ≥ k = 1 − ν ( k − 1 ) Pr � � The ν ( k ) converge to 1, so Pr S op ≥ k goes to 0. But how fast?? Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Tail Bounds for the Optimal Scheduler Theorem � S op ≤ k � = ν ( k ) Pr It follows: � � S op ≥ k = 1 − ν ( k − 1 ) Pr � � The ν ( k ) converge to 1, so Pr S op ≥ k goes to 0. But how fast?? Corollary (follows from KLE’07, EKL ’08) � � S op ≥ k ∈ O ( d k ) general task systems: Pr ( d < 1 ) � � S op ≥ k ∈ O ( d 2 k ) subcritical task systems: Pr ( d < 1 ) Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling X 0 . 2 X − → XY ֒ 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ X Y 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ X Y 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ X X Y 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ X X Y 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling X 0 . 2 X − → XY ֒ X Y 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ X X Y 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X ֒ 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε ֒ 0 . 3 Y − → YY X ֒ 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X ֒ Y X 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε X ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X Y ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X Y ֒ Y X 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε X ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X Y Y ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε X ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X Y ֒ Y 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε X ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X Y ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε X ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X ֒ X 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε X ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε X ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X ֒ X 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε X ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X ֒ 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Online Scheduling The urn model is more appropriate: 0 . 2 X − → XY ֒ 0 . 8 X − → ε ֒ 0 . 3 Y − → YY ֒ 0 . 1 Y − → X ֒ X 0 . 6 Y − → ε ֒ X ⇒ XY ⇒ XYY ⇒ XY ⇒ XX ⇒ X ⇒ ε Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Weights: An Auxiliary Notion Let v > 1 be a vector with v ≥ f ( v ) . Choose h > 1 and for all types X a weight w X with h w X = v X for all types X . X Y w X w Y Denote by W the maximum weight of a derivation. For instance: X ⇒ XY ⇒ Y ⇒ YY ⇒ Y ⇒ ε yields X X Y Y Y Y Y Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
Weights: An Auxiliary Notion Let v > 1 be a vector with v ≥ f ( v ) . Choose h > 1 and for all types X a weight w X with h w X = v X for all types X . X Y w X w Y Denote by W the maximum weight of a derivation. For instance: X ⇒ XY ⇒ Y ⇒ YY ⇒ Y ⇒ ε yields X X Y W = 2 · w Y Y Y Y Y Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
An Upper Bound for All Online Schedulers (Recall: v > 1 with v ≥ f ( v ) and h w X = v X .) One can show by a martingale argument: ≤ v X 0 � � Pr W ≥ k h k Note: Whenever S ≥ k then W ≥ k · w min . So we obtain: v X 0 v X 0 � � � � ≤ Pr W ≥ k · w min ≤ h k · w min = Pr S ≥ k v mink Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
An Upper Bound for All Online Schedulers (Recall: v > 1 with v ≥ f ( v ) and h w X = v X .) One can show by a martingale argument: ≤ v X 0 � � Pr W ≥ k h k Note: Whenever S ≥ k then W ≥ k · w min . So we obtain: v X 0 v X 0 � � � � ≤ Pr W ≥ k · w min ≤ h k · w min = Pr S ≥ k v mink Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
An Upper Bound for All Online Schedulers (Recall: v > 1 with v ≥ f ( v ) and h w X = v X .) One can show by a martingale argument: ≤ v X 0 � � Pr W ≥ k h k Note: Whenever S ≥ k then W ≥ k · w min . So we obtain: v X 0 v X 0 � � � � ≤ Pr W ≥ k · w min ≤ h k · w min = Pr S ≥ k v mink Theorem Let v > 1 with v ≥ f ( v ) . Then v X 0 � � S σ ≥ k Pr ≤ v mink for all online schedulers σ and all k ∈ N . Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
An Upper Bound for All Online Schedulers (Recall: v > 1 with v ≥ f ( v ) and h w X = v X .) One can show by a martingale argument: ≤ v X 0 � � Pr W ≥ k h k Note: Whenever S ≥ k then W ≥ k · w min . So we obtain: v X 0 v X 0 � � � � ≤ Pr W ≥ k · w min ≤ h k · w min = Pr S ≥ k v mink Theorem Let v > 1 with v ≥ f ( v ) . Let u > 1 with u ≤ f ( u ) . Then v X 0 c � � S σ ≥ k u max k ≤ Pr ≤ v mink for all online schedulers σ and all k ∈ N . Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
An Upper Bound for All Online Schedulers Example Consider the task system from the beginning: f x ( x , y ) = 0 . 2 xy + 0 . 8 f y ( x , y ) = 0 . 3 y 2 + 0 . 1 x + 0 . 6 � 1 � 1 . 4 � � One can show: f has two fixed points: and . 1 2 . 2 c ≤ 1 . 4 � � S σ ≥ k So: 2 . 2 k ≤ Pr holds for all σ . 1 . 4 k Theorem Let v > 1 with v ≥ f ( v ) . Let u > 1 with u ≤ f ( u ) . Then v X 0 c � � S σ ≥ k u max k ≤ Pr ≤ v mink for all online schedulers σ and all k ∈ N . Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
An Upper Bound for All Online Schedulers Example Consider the task system from the beginning: f x ( x , y ) = 0 . 2 xy + 0 . 8 f y ( x , y ) = 0 . 3 y 2 + 0 . 1 x + 0 . 6 � 1 � 1 . 4 � � One can show: f has two fixed points: and . 1 2 . 2 c ≤ 1 . 4 � � S σ ≥ k So: 2 . 2 k ≤ Pr holds for all σ . 1 . 4 k Theorem Let v > 1 with v ≥ f ( v ) . Let u > 1 with u ≤ f ( u ) . Then v X 0 c � � S σ ≥ k u max k ≤ Pr ≤ v mink for all online schedulers σ and all k ∈ N . Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
A Light-First Scheduler For Our Example For the upper bound we used: W ≥ k · w min . Whenever S ≥ k then � � 1 . 4 We have v = , so w min = w X . 2 . 2 We say, X is the lightest type. 0 . 2 X − → XY ֒ Light-First Scheduler: 0 . 8 X − → ε ֒ Process the lightest type (here: X ) whenever it is in the pool. 0 . 3 Y − → YY ֒ In our example, the light-first scheduler guarantees: 0 . 1 Y − → X ֒ at any time at most one X -task in the pool. 0 . 6 Hence, with the light-first scheduler: Y − → ε ֒ W ≥ 1 · w X + ( k − 1 ) · w Y . Whenever S ≥ k then Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
A Light-First Scheduler For Our Example For the upper bound we used: W ≥ k · w X . Whenever S ≥ k then � � 1 . 4 We have v = , so w min = w X . 2 . 2 We say, X is the lightest type. 0 . 2 X − → XY ֒ Light-First Scheduler: 0 . 8 X − → ε ֒ Process the lightest type (here: X ) whenever it is in the pool. 0 . 3 Y − → YY ֒ In our example, the light-first scheduler guarantees: 0 . 1 Y − → X ֒ at any time at most one X -task in the pool. 0 . 6 Hence, with the light-first scheduler: Y − → ε ֒ W ≥ 1 · w X + ( k − 1 ) · w Y . Whenever S ≥ k then Tomáš Brázdil, Javier Esparza, Stefan Kiefer, Michael Luttenberger Space-Efficient Scheduling of Stochastically Generated Tasks
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