Avoiding a bottleneck
For designers worried that the bandwidth between the processor and the PCIe switch could be a bottleneck, the PCIe switch offers a x2 configuration for the DSP that supports such a configuration, as shown in figure 2.
Fig 2: Digital video recorder/network video recorder, with x2 upstream connection.
In this example, since the connection between the DSP and the PCIe switch is now x2 wide, there isn’t any bottleneck in the system.
Another important usage model is that of a DSP farm, as shown in figure 3.
Fig 3: A typical DSP farm.
In this usage model, several DSPs are connected to a central PCIe switch through which the processing power of the system is greatly enhanced. Such a usage model is extremely attractive for vendors who want to enhance the performance of their system but the expense of implementing it. The PCIe switch and PCIe interface on the DSPs enables these designers to use a technology that is widely available and is extremely cost-competitive compared to all other technologies. Figure 3 shows a perfectly load-balanced usage model – the x8 upstream from the PCIe switch provides up to 40Gbps and the four x2 ports from the DSPs provide 40Gbps as well – so there is no bandwidth bottleneck in this system.
The flexibility that a wide portfolio of PCIe switches offers is really critical for such applications. In Figure 3, the DSP farm has only 4 DSPs, but designers need the assurance that a PCIe switch will not be a limiting factor if they want to scale their designs. If the designer decides to scale up to 12 or 16 (or more) DSPs and wants an x16 upstream port, for example, (s)he wants the PCIe switch vendor to support such configurations. Obviously, the more number of DSPs connected in a DSP farm, the higher the processing power and the more powerful such a system will be.