Chapter 1. Architecture and technical description
21
The bandwidth figures for the caches are calculated as follows:
L1 cache: In one clock cycle, two 16-byte load operations and one 16-byte store operation
can be accomplished. The value varies depending on the clock of the core, and the
formulas are as follows:
– 2.860 GHz Core: (2 * 16 B + 1 * 16 B) * 2.860 GHz = 137.28 GBps
– 3.259 GHz Core: (2 * 16 B + 1 * 16 B) * 3.259 GHz = 156.43 GBps
L2 cache: In one clock cycle, one 32-byte load operation and one 16-byte store operation
can be accomplished. The value varies depending on the clock of the core, and the
formula is as follows:
– 2.860 GHz Core: (1 * 32 B + 1 * 16 B) * 2.860 GHz = 137.28 GBps
– 3.259 GHz Core: (1 * 32 B + 1 * 16 B) * 3.259 GHz = 156.43 GBps
L3 cache: One 32-byte load operation and one 32-byte store operation can be
accomplished at half-clock speed, and the formula is as follows:
– 2.860 GHz Core: (1 * 32 B + 1 * 32 B) * 2.860 GHz = 183.04 GBps
– 3.259 GHz Core: (1 * 32 B + 1 * 32 B) * 3.259 GHz = 208.57 GBps
For the entire Power S822LC server populated with the two processor modules, the overall
bandwidths are shown in Table 1-7.
Table 1-7 Power S822LC server - total bandwidth estimates
Where:
Total memory bandwidth: Each POWER8 processor has four memory channels running at
9.6 GBps capable of writing 2 bytes and reading 1 byte at a time. The bandwidth formula is
calculated as follows:
Four channels * 9.6 GBps * 3 bytes = 192 GBps per processor module
SMP interconnect: The POWER8 processor has two 2-byte 3-lane A buses working at
6.4 GHz. Each A bus has three active lanes. The bandwidth formula is calculated as
follows:
3 A buses * 2 bytes * 6.4 GHz = 38.4 GBps
PCIe Interconnect: Each POWER8 processor has 32 PCIe lanes running at 8 Gbps
full-duplex. The bandwidth formula is calculated as follows:
Thirty-two lanes * 2 processors * 8 Gbps * 2 = 128 GBps
Total bandwidths
8335-GCB
20 cores @ 2.860 GHz
16 cores @ 3.259 GHz
L1 (data) cache
2,746 GBps
2,503 GBps
L2 cache
2,746 GBps
2,503 GBps
L3 cache
3,661 GBps
3,337 GBps
Total memory
230 GBps
230 GBps
PCIe Interconnect
128 GBps
128 GBps
Summary of Contents for S822LC
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