RIStAL Centre de Recherche en Informatique, Signal et Automatique - - PowerPoint PPT Presentation

Centre de Recherche en Informatique, Signal et Automatique de Lille

RIStAL

JNP : Symbolic WCET Computation

Clément Ballabriga, Julien Forget, Giuseppe Lipari Real-Time System Symposium, Paris, December 2017

1

Parametric WCET

Parametric Worst-case execution time (PWCET) produces a formula that represents the worst-case execution time of the program as a function of user-defined parameters Examples of parameters : Number of iterations in a loop depends on the size of a matrix Which alternative is taken in a if-then-else depends on an input variable The program uses an external library function, and the function WCET is still unknown

2

Our Method at a glance

Control Flow Graph → Control Flow Tree → Formula

b1 b2 b3 b4 b5 b6 Seq Loop(b1) b1 b5 b1 Alt b3 Seq b6 Loop(b2) b2 Seq b2 b4 w(Loop(b2)) = (⊤, pack(⊤, {6}, k) ⊕ (⊤, {2}))

Performance faster than ILP almost the same precision

3

What can you do with it ?

Offline : Fast exploration of the space of parameters A component-based methodology Online : Adaptive systems ! The formula parameters are variable inputs We can instantiate the formula with the actual value of the input before executing the code, so to estimate its execution time Post-doc position available on this topic !! Looking forward to meet you at the poster !!

4