Adding deadlines
Wednesday, April 28, 2010
1:56 PM
Adding deadlines (SLA's)
Alas, clouds typically support interactive queries
One needs to finish each one by a given deadline. 
Suppose you have 40  10-unit tasks arrive with the same deadline of 20 units. 
Considering context switching to have 5% overhead: 
Running on one machine, overhead is 5% of total computation time of 400 units, total is 420 units, doesn’t meet deadline! 
Running on 20 machines, overhead 5%*total time of 40 units, total time 40*1.05=42 units, total power proportional to 42*20 = 840  units. 
Running on 40 machines meets deadline, 
overhead near 0, total time 10 units; total power proportional to 40*10=400 units. 
There is a break-even point between 20 and 40 
machines that balances overhead against deadline!