No of course most workloads aren't using all 4 cores. All the Javascript ones are even single threaded (when Anand says Kraken is multithreaded he is wrong, try running it yourself and you'll see it's purely single threaded). Unfortunately the masses will assume otherwise and believe that one Saltwell core outperforms two Cortex-A9 cores put together. Often times you will have two threads active but while one does a lot of work the other only does a little work, and this scenario is well suited to HT instead of two cores.
Maybe Anand should have included core utilization graphs alongside the power numbers. I don't know why review sites never do this. In Windows it should be especially easy.
The companion does still help with more than idle, look at the power consumption charts, they're not straight lines. Utilization is constantly ramping up and down. I don't know where the companion core kicks in, AFAIK it'd be below 500MHz. So it'll be beneficial even for some parts of these workloads where the CPU is being used. Unfortunately Tegra 3's model only lets you use the companion core when nothing else is used (that's really all they could do with Cortex-A9), so it's pretty limited. Still, you'd get some tasks that are doing the heavy lifting elsewhere like video or other heavily accelerated processes, but they still need to do something on the CPU outside of idle it all the time. Here the low power core helps.
4 core Cortex-A9s (and pure Cortex-A15 systems) are difficult to schedule well with asynchronous workloads, because the entire chip runs at the same frequency and voltage. So your choice is to run more cores at a lower frequency or fewer cores at a higher frequency. If you make a bad decision here (or worse, run all cores at a high frequency) then you'll get bad results. I don't know how good of a job MS has done optimizing WinRT for this sort of workload, but if they can't support the companion core mode at all I'm not optimistic). This is all the more reason why someone like Anand should include with their review side by side information listing what cores are active and what the frequency is. It'd be just as interesting for Atom which has HT and Turbo, so you can see what it's profile is like for utilization of both, and how well Windows is scheduling threads vs cores. With stuff like this you could do some real analysis. Unfortunately people are more interested in pissing contests than real analysis and that's what review sites cater to.
Personally, I find big.LITTLE a lot more attractive because you can run a small number (1-2) of strong Cortex-A15 cores along side active (1-4) Cortex-A7 cores, which will do well with asynchronous workloads the same way Intel's HT does. Bizarrely, rumors indicate that Silvermont is actually dropping HT, which IMO is Atom's number one trump card (although it has some other advantages). We'll have to see how that all plays out. Particularly if four Silvermont cores will be totally asynchronous themselves.
