All through class I kept being astounded at how complex implementing cache coherency is. Even in our simple model, there are a large number of steps that need to be performed. Doesn't this negatively affect performance, and the benefits of using a cache in the first place? Specifically, how much slower is using a processor with cache coherence than without?
@sbly, sure this will take away from the performance of a cache, but it is still a significant speedup from a system with out a cache. As the link @cardiff seems to be dead, I would simply say its hard to say how much slower a processor with cache coherence is. This is because without cache coherence, a lot of things would be trash as we as the programmers have a basic assumption of how the memory system works. As the cache abstraction should not really change our thought process of how memory works, having no cache coherence can really cause some problems. Therefore, I think its hard and useless to compare the speed difference between a system that works with coherence, and a system that has issues without coherence.
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cardiff
I believe I have fixed the dead link in my comment above. Thanks @ycp for pointing out the problem.
All through class I kept being astounded at how complex implementing cache coherency is. Even in our simple model, there are a large number of steps that need to be performed. Doesn't this negatively affect performance, and the benefits of using a cache in the first place? Specifically, how much slower is using a processor with cache coherence than without?
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Of course it depends on the specific protocol, but based on this evaluation of the cost of cache coherence protocols, it seems that 35% slower might be a reasonable figure for MESI.
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@sbly, sure this will take away from the performance of a cache, but it is still a significant speedup from a system with out a cache. As the link @cardiff seems to be dead, I would simply say its hard to say how much slower a processor with cache coherence is. This is because without cache coherence, a lot of things would be trash as we as the programmers have a basic assumption of how the memory system works. As the cache abstraction should not really change our thought process of how memory works, having no cache coherence can really cause some problems. Therefore, I think its hard and useless to compare the speed difference between a system that works with coherence, and a system that has issues without coherence.
This comment was marked helpful 0 times.
I believe I have fixed the dead link in my comment above. Thanks @ycp for pointing out the problem.
This comment was marked helpful 0 times.