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""" centralserver.py
A time-shared computer consists of a single
central processing unit (CPU) and a number of
terminals. The operator of each terminal `thinks'
for a time (exponential, mean 100.0 sec) and then
submits a task to the computer with a service time
(exponential, mean 1.0 sec). The operator then
remains idle until the task completes service and
returns to him or her. The arriving tasks form a
single FCFS queue in front of the CPU.
Upon leaving the CPU a task is either finished
(probability 0.20) and returns to its operator
to begin another `think' time, or requires data
from a disk drive (probability 0.8). If a task
requires access to the disk, it joins a FCFS queue
before service (service time at the disk,
exponential, mean 1.39 sec). When finished with
the disk, a task returns to the CPU queue again
for another compute time (exp, mean 1.$ sec).
the objective is to measure the throughput of
the CPU (tasks per second)
"""
from SimPy.Simulation import *
## from SimPy.SimulationTrace import *
import random as ran
## Model components ------------------------
class Task(Process):
""" A computer task requires at least
one use of the CPU and possibly accesses to a
disk drive."""
completed = 0
rate = 0.0
def execute(self,maxCompletions):
while Task.completed < MaxCompletions:
self.debug(" starts thinking")
thinktime = ran.expovariate(1.0/MeanThinkTime)
yield hold,self,thinktime
self.debug(" request cpu")
yield request,self,self.sim.cpu
self.debug(" got cpu")
CPUtime=ran.expovariate(1.0/MeanCPUTime)
yield hold,self,CPUtime
yield release,self,self.sim.cpu
self.debug(" finish cpu")
while ran.random() < pDisk:
self.debug(" request disk")
yield request,self,self.sim.disk
self.debug(" got disk")
disktime=ran.expovariate(1.0/MeanDiskTime)
yield hold,self,disktime
self.debug(" finish disk")
yield release,self,self.sim.disk
self.debug(" request cpu")
yield request,self,self.sim.cpu
self.debug(" got cpu")
CPUtime=ran.expovariate(1.0/MeanCPUTime)
yield hold,self,CPUtime
yield release,self,self.sim.cpu
Task.completed += 1
self.debug(" completed %d tasks"%(Task.completed,))
Task.rate = Task.completed/float(self.sim.now())
def debug(self,message):
FMT="%9.3f %s %s"
if DEBUG:
print FMT%(self.sim.now(),self.name,message)
## Model ------------------------------
class CentralServerModel(Simulation):
def run(self):
self.initialize()
self.cpu = Resource(name='cpu',sim=self)
self.disk = Resource(name='disk',sim=self)
for i in range(Nterminals):
t = Task(name="task"+`i`,sim=self)
self.activate(t,t.execute(MaxCompletions))
self.simulate(until = MaxrunTime)
return (self.now(),Task.rate)
## Experiment data -------------------------
Nterminals = 3 ## Number of terminals = Tasks
pDisk = 0.8 ## prob. of going to disk
MeanThinkTime = 10.0 ## seconds
MeanCPUTime = 1.0 ## seconds
MeanDiskTime = 1.39 ## seconds
ran.seed(111113333)
MaxrunTime = 20000.0
MaxCompletions = 100
DEBUG = False
## Experiment
result = CentralServerModel().run()
## Analysis/output -------------------------
print 'centralserver'
print '%7.4f: CPU rate = %7.4f tasks per second'%result
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