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System parameters:
Remarks: The BlueGene/L is the first in a new generation of systems made by IBM for very massively parallel computing. The individual speed of the processor has therefore been traded in favour of very dense packaging and a low power consumption per processor. The basic processor in the system is a modified PowerPC 400 at 700 MHz. Two of these processors reside on a chip together with 4 MB of shared L3 cache and a 2 KB L2 cache for each of the processors. The processors have two load ports and one store port from/to the L2 caches at 8 bytes/cycle. This is half of the bandwidth required by the two floating-point units (FPUs) and as such quite high. The CPUs have 32 KB of instruction cache and of data cache on board. In favourable circumstances a CPU can deliver a peak speed of 2.8 Gflop/s because the two FPUs can perform fused multiply-add operations. Note that the L2 cache is smaller than the L1 cache which is quite unusual but which allows it to be fast. The packaging in the system is as follows: two chips fit on a compute card with 512 MB of memory. Sixteen of these compute cards are placed on a node board of which in turn 32 go into one cabinet. So, one cabinet contains 1024 chips, i.e., 2048 CPUs. For a maximal configuration 64 cabinets are coupled to form one system with 65,356 chips/130,712 CPUs. In normal operation mode one of the CPUs on a chip is used for computation while the other takes care of communication tasks. In this mode the Theoretical Peak Performance of the system is 183.5 Tflop/s. It is however possible when the communication requirements are very low to use both CPUs for computation, doubling the peak speed; hence the double entries in the System Parameters table above. The number of 360 Tflop/s is also the speed that IBM is using in its marketing material. The BlueGene/L possesses no less than 5 networks, 2 of which are of interest for inter-processor communication: a 3-D torus network and a tree network. The torus network is used for most general communication patterns. The tree network is used for often occurring collective communication patterns like broadcasting, reduction operations, etc. The hardware bandwidth of the tree network is twice that of the torus: 350 MB/s against 175 MB/s per link.
BlueGene/P
One board in the system carries 32 quad-core chips while again 32 boards can be
fitted in one rack with 4,096 cores. A rack therefore has a Theoretical Peak
Performance of 13.9 Tflop/s. The IBM Press release sets the maximum number of
cores in a system to 884,736 in 216 racks and a Theoretical Peak Performance of
3 Pflop/s. The higher bandwidth of the main communication networks (torus and
tree) also goes up by a factor of about 2 while the latency is halved. \nal In both the BlueGene/L and /P the compute nodes runs a reduced-kernel type of Linux to reduce the OS-jitter that normally occurs when very many nodes are involved in computation. Interface nodes for interaction with the users and providing I/O services run a full version of the operating system.
Measured Performances: |