5.3. The Effect of the Relaxation of Power Constraint
Impact of Four-activation-window Constraint Compared
to Relaxed-ClosePage policy, the performance of
Restrict-ClosePage policy is limited by Four-activationwindow
constraint because any memory request requires an
activation/precharge while the constraint limits the activation
frequency [24]. According to the value of tRRD and tFAW
shown in Table 3, there can be 5.3- (=tFAW
tRRD ) activations in
a tFAW if no Four-activation window constraint is applied.
In other words, DRAM loses 25% (=tFAW−4×tRRD
tFAW ) activation
bandwidth due to the tFAW constraint. As Half-DRAM alleviates
the power constraints, the activation rate can be improved
accordingly. To verify the advantage of Half-DRAM, we rerun
the simulation and the results are shown in Figure 11a.
The average speedup in Half-DRAM-1Row is 6.9%. Compared
to the results of Relaxed-Close Policy is applied (Figure
10a), Half-DRAM-1Row has even higher performance
improvement, which unsurprisingly comes from the relaxation
of four-activation-window constraint. In particular, test3 has
11.8% improvement as the requests going to the same rows
that originally have to wait for the row re-activation can now