Interpret this CPU usage graph- iMac i7 / EyeTv export

Hi folks,

Just got my i7 iMac the other day. Not all apps use all cores (as expected), but I'm interested to understand this one. Export MPEG2 (TS stream) from EyeTv to AppleTv format (I think it uses quicktime but can't tell).

Check out the pic. Now there are 4 real cores, but OSX is showing the 8 virtual cores. Anyway, given there are 4 cores, what does it imply to have around 50% total utilisation? Two threads? Four threads?

I notice that BOINC (einstein@home) only gets up to total utilisation when its running 8 threads. Does this mean that EyeTv (quicktime) is asking for number of cores and then creating that many threads? EyeTv is only showing one line time in Activity Monitor at around 400%.

Can these utilisation graphs actually be trusted when the 8 cores are virtual?

 

But why only 50% of total CPU? The graph is pretty much steady and looks like the above the whole time during the export. No core reaches 100%. Considering that einstein also only uses 50% if 4 threads are launched and bearing in mind that there are only 4 real cores, then it appears that either
a) you can't rely on these graphs once they reach at least 50% processor utilisation because they don't interpret the hyperthreading properly OR
b) You can't max out a real core with one thread. You need two. The hyperthreading is "hard coded". For all practical purposes you have an 8 core machine and need 8 threads to maximise performance.

I think I need to check some PC hardware sites to find the answer.

 

Thanks Makosuke, I like the theory. The only problem with this is that why is it that when I run Boinc (einstein@home) with 8 threads, it maxes out all 8 "cores" to 100%, each reporting just under 100% utilisation (total 800%)? According to your theory, each thread should only be running at around 50% and shown as such on the graph.

I agree that the difference in actual work done between a core (2 virtual cores) running one thread or two is not double. Of course the core is being shared and therefore one cannot hope for double performance if two threads are being run on the one physical core. But I note that several people reckon they get ~30% more actual work done in BOINC with hyperthreading enabled than when it is not. That means that the difference between the graph I posted above, where each virtual core is running ~50% (total 400%) and having 8 threads with each virtual core running 100% is a real positive difference and a benefit, but of course it is not double the performance.

My conclusions is that with virtualisation, CPU utilisation graphs are not accurate. I wish there was a way to graph CPU utilisation as a percentage of possible throughput, but of course this would vary according to the type of work being done.

I also think that EyeTV exports (Quicktime?) could be optimised better for an i7 to further utilise hyperthreading on i7, although I agree the difference would not be huge, especially if other apps and tasks are running.

Any other ideas?