23

Requests 

Requests 

from Web 

from Web 

Switch 

Switch 

Coscheulded 

Main 

Main 

Remote 

Remote 

Cache 

Cache 

r 

Recv 

Send 

r 

e 

e 

y 

y 

a 

VIA 

a 

r   L 

r   L 

e s  Disk 

Disk 

e s 

U  Helper 

Coscheulded 

Helper  U 

Remote 

Remote 

Cache 

Cache 

Send 

Recv 

r 

r 

e 

e 

y 

y 

a 

a 

l   L 

Coscheduling Modules 

Coscheduling Modules 

l   L 

e 

e 

Linux Scheduler 

r n 

Linux Scheduler 

r n 

e 

e 

K 

K 

Fig. 3.2. Coscheduled PRESS Model

node, the corresponding process at that node is coscheduled with the hope that both the

sender and receiver are scheduled simultaneously for efficient communication. Thus, in

our model, whenever a remote cache read request arrives at the corresponding send queue

of the remote cache send process, the remote cache send process pushes this request to

the network using VIA and waits (spins) until the response arrives from the service node.

When the request arrives at the service node (actually in the NIC), the corresponding

remote cache recv process is scheduled using the DCS coscheduling policy.

Note that without this coscheduling scheme, in the PRESS model, the remote cache recv

process has to wait until the Linux scheduler assigns the CPU to it. The remote cache recv

process in the service node sends the requested file from its local cache to the initial node

whose remote cache send process is also coscheduled. If there is no jobs to process, the

remote cache recv process returns to the blocking state. After receiving the reply, the