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Low-Power Techniques for Network-on-Chip
(F2 and F3) for the body flits ensures the duration of staying in idle condition.
Although dynamic power with higher frequency operations is expected to
be more than the power with original clock frequency operation, the overall
network power may be less because idle operation and head flit transmission
have different switching activities even though they operate with the same
frequency. Increasing boosting clock frequency results in more idle cycles
since the body flits are transmitted with higher frequency.
6.4.2.1 History-Based DFS
Network workload exhibits transient fluctuation and long-term transitions.
In order to filter out transient fluctuations from link utilization and to predict future communication workload, a history-based algorithm is used for
DFS scheme and is described below. In applying DFS to a system, how to
predict future workload with reasonable accuracy is a critical problem. This
requires knowing how many packets will traverse a link at any given time.
Two issues complicate this problem. First, it is not always possible to accurately predict future traffic activities. Second, a subsystem can be preempted
at arbitrary times due to user and I/O device requests, varying traffic beyond
what was originally predicted. In order to estimate future workload, link
utilization is adopted as an indicator, which is a direct measure of traffic
through a link in each unit time. Lower link utilization reflects more idle
cycles in a link caused by network congestion with heavy traffic or sparse
workload in the incoming port. Conversely, higher link utilization implies
that more active cycles in a link pass flits to the destination router. The link
utilization is measured by sampling a link at a given time during a predefined control period (Tc). The direct link utilization is defined, where k
denotes the number of samples in Tc time period:
∑
k
u(t)
U
t=1
L (n) =
(6.12)
k
where:
⎧1 If there is link trafficin cyclet
⎪
u(t) = ⎨
⎩ ⎪ 0 If there is no link trafficin n cyclet
The direct estimator only measures the link utilization whether a link is
occupied or not. It does not consider the number of flits traversing through a
link during the given time. For instance, even though the link utilizations are
the same in time durations Δt 1 and Δt 2 , the number of flits passing through
the link can be different according to the clock frequency of the router at
those times.
Low-Power Techniques for Network-on-Chip
(F2 and F3) for the body flits ensures the duration of staying in idle condition.
Although dynamic power with higher frequency operations is expected to
be more than the power with original clock frequency operation, the overall
network power may be less because idle operation and head flit transmission
have different switching activities even though they operate with the same
frequency. Increasing boosting clock frequency results in more idle cycles
since the body flits are transmitted with higher frequency.
6.4.2.1 History-Based DFS
Network workload exhibits transient fluctuation and long-term transitions.
In order to filter out transient fluctuations from link utilization and to predict future communication workload, a history-based algorithm is used for
DFS scheme and is described below. In applying DFS to a system, how to
predict future workload with reasonable accuracy is a critical problem. This
requires knowing how many packets will traverse a link at any given time.
Two issues complicate this problem. First, it is not always possible to accurately predict future traffic activities. Second, a subsystem can be preempted
at arbitrary times due to user and I/O device requests, varying traffic beyond
what was originally predicted. In order to estimate future workload, link
utilization is adopted as an indicator, which is a direct measure of traffic
through a link in each unit time. Lower link utilization reflects more idle
cycles in a link caused by network congestion with heavy traffic or sparse
workload in the incoming port. Conversely, higher link utilization implies
that more active cycles in a link pass flits to the destination router. The link
utilization is measured by sampling a link at a given time during a predefined control period (Tc). The direct link utilization is defined, where k
denotes the number of samples in Tc time period:
∑
k
u(t)
U
t=1
L (n) =
(6.12)
k
where:
⎧1 If there is link trafficin cyclet
⎪
u(t) = ⎨
⎩ ⎪ 0 If there is no link trafficin n cyclet
The direct estimator only measures the link utilization whether a link is
occupied or not. It does not consider the number of flits traversing through a
link during the given time. For instance, even though the link utilizations are
the same in time durations Δt 1 and Δt 2 , the number of flits passing through
the link can be different according to the clock frequency of the router at
those times.