Industry Expert Blogs

Joe has devoted his career to understanding and designing cache coherent systems and has been granted over 60 patents on the subject. For the past four years, he has been Chief Architect at NetSpeed, a developer of network-on-chip SoC interconnect.

Why did cache and coherency catch your interest in the first place?
There are many, many aspects of caches that are interesting, and I find them all very interesting. I sometimes joke that caches are just a performance tweak. They are architecturally transparent. And so, they improve your performance but they are supposed to appear as if they don't even exist. That makes both the building and the verification of them complicated because, how do you verify something that you can't actually detect whether it's there or not---if is transparent? You end up testing that it's transparent. It's kind of an interesting problem. Coherency is very interesting. I find it analogous to some of these strategy board games like chess or go in that the rules are very simple. Many protocols are only four coherent states, ---modified, exclusive, shared, and invalid ---and yet there is an infinite number of variations in terms of design trade-offs and complexity. And even though you start off with some very simple principles you can spend a lifetime mastering it.

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