I think another huge issue is the combination of general-purpose/multi-tenant computing, especially with virtualization in the mix, and cache. Improvements gain

I think another huge issue is the combination of general-purpose/multi-tenant computing, especially with virtualization in the mix, and cache. Improvements gained from masking memory latency by issuing instructions from more thread execution contexts are suddenly lost when each of those thread contexts is accessing a totally different part of memory and evicting the cache line that the next thread wanted anyway. In many ways barrel processing and hyperthreading are remarkably similar to VLIW - they're two very different sides of the same coin. At the end of the day, both work well for situations where multiple simultaneous instruction streams need to access relatively small amounts of adjacent data. Realtime signal processing, dedicated databases, and gaming are obvious applications here, which I think is why VLIW has done so well in DSP and hyperthreading did well in gaming and databases. Once the simultaneous instruction streams are accessing completely disparate parts of main memory, it all blows up. Plus, in a multi-tenant environment, the security issues inherent to sharing even more execution state context (and therefore side channels) between domains also become untenable fairly quickly.