Things should be faster with 8 threads instead of 4. Not 2x faster of course as you'll be running two threads per physical core (that's what hyperthreading does). Exactly how much faster will depend on what you're rendering.

Hello, thinking about buying a couple of core i7s nodes...
I heard that it is better to use same architecture processors for distributed rendering. So will I have some notable miss-correspondence if i render the sequence with core 2 quad and core i7???

thanks

Hello Guys,

I think it is time to say something about that CPU usage in multi-threaded application. Many of our users look at the CPU usage as an indication of multi-threading performance. This is inaccurate. For example, a badly written application might take 100% of your CPU because of bad synchronization between threads (spinlocks will take CPU time without producing any useful work, for example).

To measure the performance of a multi-threaded application, simply divide wall clock time it takes to render your image using N threads by the wall time it takes to render your image using 1 thread. The highest the number you get, the more efficient your program is. If the number you get is N (the number of threads itself) then you have a linear performance increase, and that is a maximum for normal programs. This maximum performance increase is seldom seen in real word programs (I am not talking about a Mandelbrot drawing application or some other marketing experiment) and the reason is a) bad design and b) synchronization or both. Synchronization can even be necessary at the kernel level (think about 2 threads waiting for some I/O) so it might be very difficult to augment threading performance in some particular contexts (it will be pegged at a lower level on your system).

Now, to achieve the linear performance increase, your program has to be pegged to 100% all the time, so high CPU usage is already a good indication but it is really only half of the answer. In other words, it might be possible that a program A will run faster at 50% CPU usage than a program B running at 100% CPU usage, and producing the same result. So caution is advised when measuring performance in multi-threaded applications.

How does that affect your daily work ? Were you about to buy twice as many cores to render twice faster and deliver that project right on time? That might be slightly optimistic :)

  -- aghiles