28

Web Server  

Web Server  

Call VIA functions 

r ing a doorbell 

VipRecvDone 

VipRecvDone 

(),  

(),  

VipRecvWait 

VipRecvWait 

(),  

(),  

VipSendWait 

VipSendWait 

() 

() 

S

S

c

c

h

h

e

e

d

d

u

u

l

l

e

e

r

r

Co 

Co 

Scheduler 

Scheduler 

Module 

Module 

Select  a process  

running queue 

by calling goodness() 

wait queues 

DMA 

DMA 

NCP 

NCP 

Intelligent 

Intelligent 

NIC 

NIC 

NIC Processor 

NIC Processor 

Fig. 3.4. Three Layers of the Simulator

is determined by adding up the numerical values of three priority types; 1) Super user

controlled real time priority, 2) User assigned priority, and 3) System assigned dynamic

priority [17]. When a coscheduling algorithm is applied, however, the Linux scheduler

receives the process pointer from the coscheduling module. The coscheduling module

chooses the next running process based on the underlying coscheduling policy [27, 3].

Different coscheduling policies can be simulated using appropriate parameters. Finally,

the coscheduled Web server model is simulated to capture all the functionalities. It is

possible to specify the Web server configuration in terms of number of nodes, cache size,

and many other parameters. In the simulator, these three layers are synchronized by

events of csim. For instance, when a process finishes its time quantum, it sends an event

to the scheduler. The scheduler calculates the next running process by calling goodness()

function. Then, the simulator sends an event to the chosen process.