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Support Question:
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I am getting strange PerformanceTest results for the CPU test. I have a Intel Pentium4 running at 2.8Ghz (or 3.06Ghz) that gets better scores in the CPU test than the new 3.2Ghz P4.
The 3.06Ghz CPU has a front side bus (FSB) speed of 533Mhz and 512KB of cache. The 3.2Ghz P4 has a FSB of 800Mhz and 1MB of cache. So the new CPU should get better scores than the old ones.
Answer:
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There are many other factors that effect performance besides clock speed. In this case it is probably the extended 31 stage CPU pipeline in the 3.2Ghz Prescott didn't work as well as the 20 stage pipeline in the previous Intel CPUs (like the Northwood). It is well documented that long pipelines are not always good for performance. The larger cache might also be slightly slower in speed despite being bigger in size.
Longer pipelines are good for increasing the clock speed however. But in this case the slight increase in clock speed doesn't seem to compensate for the inefficient long pipeline.
What are CPU pipelines?
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Pipelining is an implementation technique used by CPU manufacturers in which multiple instructions are overlapped in execution. It also exploits parallelism among instructions in a sequential instruction stream.
Unfortunately the CPU often needs to make a guess about what code is going to executed in the future in order to load up the pipeline with new instructions. If it guesses incorrectly or the result of one instruction depends on the results of a previous instruction, the pipeline starts to become inefficient and overall performance decreases.
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David
PassMark
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I am getting strange PerformanceTest results for the CPU test. I have a Intel Pentium4 running at 2.8Ghz (or 3.06Ghz) that gets better scores in the CPU test than the new 3.2Ghz P4.
The 3.06Ghz CPU has a front side bus (FSB) speed of 533Mhz and 512KB of cache. The 3.2Ghz P4 has a FSB of 800Mhz and 1MB of cache. So the new CPU should get better scores than the old ones.
Answer:
----------
There are many other factors that effect performance besides clock speed. In this case it is probably the extended 31 stage CPU pipeline in the 3.2Ghz Prescott didn't work as well as the 20 stage pipeline in the previous Intel CPUs (like the Northwood). It is well documented that long pipelines are not always good for performance. The larger cache might also be slightly slower in speed despite being bigger in size.
Longer pipelines are good for increasing the clock speed however. But in this case the slight increase in clock speed doesn't seem to compensate for the inefficient long pipeline.
What are CPU pipelines?
----------------------------
Pipelining is an implementation technique used by CPU manufacturers in which multiple instructions are overlapped in execution. It also exploits parallelism among instructions in a sequential instruction stream.
Unfortunately the CPU often needs to make a guess about what code is going to executed in the future in order to load up the pipeline with new instructions. If it guesses incorrectly or the result of one instruction depends on the results of a previous instruction, the pipeline starts to become inefficient and overall performance decreases.
-------
David
PassMark
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