Kevin Closson's Blog: Platforms, Databases and Storage

2 Responses to “An 8GHz Pentium Processor”

1. 1 Noons January 22, 2007 at 11:52 pm

   quick request for a blog entry:

   I know you address it somewhat in the book, but here goes anyway:

   in a NUMA multi-quad, don’t you inherently get a high CPI whenever there is a mem sync clash across quads? How does that impact on things like latches, for example? I never understood properly that section of the book and since you might know a thing or two about the subject I thought I’d ask? 😉

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2. 2 kevinclosson January 23, 2007 at 12:25 am

   Hi Noons,

   Yes, I’ll need to discuss coherency misses. It all depends on how latches are implemented. In short, using a simple test and set sort of spinlock, NUMA suffers with heavily contended latches. In the end, however, it all depends on how “lumpy” the memory is. If a remote memory write is some 100x more costly than a local memory write, then normal spinlock just don’t work–well, they don’t fail but they don’t scale 🙂

   I’ll make sure to cover some of those goodies.

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