This need not be the case, we have demonstrated speedups of up to a factor of 70 when using 115 processors on a 128-processor SGI Origin 2000. This raises the question of why so many people have a poor opinion of this paradigm. Older architectures had fewer processors, and in general the processors were slower. Codes run on these machines would not show great speedup due to the limited numbers of processors. When these programs were taken to newer machines with larger numbers of faster processors, they frequently needed additional tuning.
Many people equate loop-level parallelism with automatic parallelization .
In general, it is true that automatic parallelization does not produce high levels of scalability, but it is incorrect to assume that it is the only way to use this paradigm. Just as with message-passing code, it can take work and skill to show high levels of scalability. However, not everyone has either the time or the skills to do this work, and others were discouraged from even trying and instead went in other directions. With this change, he was able to show good scalability to at least 50 processors on a 64-processor system. Therefore, it is quite important to keep the system from paging.