Issues/Characteristics for Architecture(Hardware) and Software of PetaFLOPSMachines

There were particularly fruitful interactions between architecture and application groups. We can make the following general remarks on characteristic features of PetaFLOPS scale applications.

1. We need to establish a common ``language'' (set of terms) to discuss memory hierarchy/parallelism and communication in a hardware/software /algorithmic implementation neutral fashion. We recommend a near-term activity to refine initial steps begun here to define applications for architecture and software communities. This implementation neutral description of applications and architectures should also help discussions between software and architecture communities. The need for this agreed terminology was highlighted by our discussions with the architecture group where latter noted that application scientists described the computational structure of their problem inappropriately-using, for instance, the language of MIMD distributed memory machines when issues were more general and reflected memory hierarchy. As the target PetaFLOPS machine could have a mix of these architectures, a distributed set of hierarchical memory nodes, translating application scientist specifications into PetaFLOPS designs led to vigorous confused debate.
2. Our discussions with architecture group isolated several classes of machines-three based on memory hierarchy processor trade-offs and others based on memory size and I/O requirements.
3. We made a list of architectural features, which are shown in Tables 4.2, 4.3, and 4.4. These were used as a guide in preparing exemplar application discussions in Section 4.4.

   

   

   

   

4. We recommend that once a better framework is agreed (see item 1.), that ``domain experts'' be asked to refine our study (as begun in Section 4.4) in a broader range of potential PetaFLOPS scale applications. Potential application domains are already given in Table 4.1.
5. We identified a general rule for time stepped algorithms (Section 4.4.1).

   

   *Put here memory needed at a GigaFLOPS performance.

   for fixed total simulation time, but if needed (as often one does) to increase total simulated time. This rule predicts a memory size of 30 terabytes is appropriate for a PetaFLOPS machine if 1 gigabyte is appropriate for a GigaFLOPS machine. This estimate is consistent with NASA's aerospace predictions in Figure 4.1.

6. Current ``rule'' memory (bytes) = performance (FLOPS) is modified because up to ``now,'' solving problems has been constrained by machine size and so one scales problem ``blindly.'' On the other hand, the PetaFLOPS machines will solve real problems constrained by the ``physics'' of the situation.
7. Some interesting characteristics of a PetaFLOPS machine are
   • PetaFLOPS machines will do in five minutes what it takes GigaFLOPS machines 10 years to do
   • (grid size)
   • years video

     books

     megapixel images

     compressed images

8. Some PetaFLOPS applications are somewhat less demanding on hardware characteristics than today's problems (e.g., they are applications with a lot of compute needs and this implies lower internode communication bandwidth to node compute power ratio).
9. It is interesting to consider real-time applications so that PetaFLOPS performance is required to keep up with the machine and people in loop (e.g., defense simulation and control).
10. Many real-world simulations need PetaFLOPS because problems have multiple length scales.
11. All members of the applications working group felt that PetaFLOPS central supercomputers should be accompanied by the natural scaling TeraFLOPS level workstations distributed among the users.