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Lowest−Latency−Time−First (LLTF)
First−Latency−Time−First (FLTF)
1000
1000
ACO
PSO
GA
ACO
PSO
GA
800
800
600
600
400
400
200
200
0
0
1000
2000
3000
4000
5000
6000
7000
8000
9000 10000
1000
2000
3000
4000
5000
6000
7000
8000
9000 10000
Number of jobs
Number of jobs
Latency−Time−In−Round (LTIR)
1000
ACO
PSO
GA
800
600
400
200
0
1000
2000
3000
4000
5000
6000
7000
8000
9000 10000
Number of jobs
Fig. 2. Response time as the number of jobs increases
the population size. The number of messages to send through the network for each al-
gorithm directly impacts the response time to the user. This is because for each message
sent to query about hosts availability, latencies from datacenters a
ect the answers.
The proposed ACO and PSO, however, make less use of network resources than GA,
being in some cases PSO the one which sends less network messages. The number of
messages to send by ACO depends of the maximum number of steps that an ant carries
out to allocate its associated VM. For example, when the maximum number of steps
is equals to 8, ACO sends a maximum of 8 messages per VM allocation. Moreover,
when ACO finds an idle host, it allocates the current VM and does not perform any
further step. This reduces the total number of network messages sent. On the other
hand, the number of network messages to send by PSO depends of the neighborhood
size, which is also equals to 8, i.e., PSO sends a maximum of 8 messages per VM
allocation. Furthermore, like ACO, when PSO finds an idle host, it allocates the current
VM and does not make any further move. This also reduces the total number of network
messages sent, and therefore, the total latency that influences the user response time.
Another observations from the subfigures included in Figure 2 are that when the
LLTF policy is used combined with PSO, ACO and GA, the response time decreases
with respect to FLTF and LTIR policies. This happens because most VMs are created
in datacenters with lower latencies. For example, when the LLTF policy is used and
the number of jobs to be executed is increased from 1,000 to 10,000, the response
time varied between (71-661), (72-661), and (191-780) minutes, for PSO, ACO and
GA, respectively. On the other hand, when the FLTF policy is used at the broker level,
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