Specifications
5102ch02.fm Draft Document for Review May 12, 2014 12:46 pm
38 IBM Power System S822 Technical Overview and Introduction
Next CDIMM pair is identical and installed at C25 and C27.
Next CDIMM pair is identical and installed at C20 and C22.
Next CDIMM pair is identical and installed at C28 and C30.
2.2.3 Memory bandwidth
The POWER8 processor has exceptional cache, memory, and interconnect bandwidths.
Table 2-4 shows the maximum bandwidth estimates for a single core on the Power S822
system.
Table 2-4 Power S822 single core bandwidth estimates
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 formula
is as follows:
3.42 GHz Core: (2 * 16 B + 1 * 16 B) * 3.42 GHz = 164.2 GBps
3.89 GHz Core: (2 * 16 B + 1 * 16 B) * 3.89 GHz = 186.7 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:
3.42 GHz Core: (1 * 32 B + 1 * 16 B) * 3.42 GHz = 164.2 GBps
3.89 GHz Core: (1 * 32 B + 1 * 16 B) * 3.89 GHz = 186.7 GBps
L3 cache: One 32-byte load operation and one 32-byte store operation can be
accomplished at each clock cycle and the formula is as follows:
3.42 GHz Core: (1 * 32 B + 1 * 32 B) * 3.42 GHz = 218.9 GBps
3.89 GHz Core: (1 * 32 B + 1 * 32 B) * 3.89 GHz = 249.0 GBps
For the whole system, considering a Power S822 populated with two processor modules, the
overall bandwidths are as follows:
Table 2-5 Power S822 total bandwidth estimates
Single Core Power S822 Power S822
1 core @ 3.42 GHz 1 core @ 3.89 GHz
L1 (data) cache 164.2 GBps 186.7 GBps
L2 cache 164.2 GBps 186.7 GBps
L3 cache 218.9 GBps 249.0 GBps
Total Bandwidths Power S822 Power S822
20 cores @ 3.42 GHz 12 cores @ 3.89 GHz
L1 (data) cache 3,284 GBps 2,240 GBps
L2 cache 3,284 GBps 2,240 GBps
L3 cache 4,352 GBps 2,988 GBps
Total Memory 384 GBps 384 GBps
SMP Interconnect 38.4 GBps 38.4 GBps