Question About Rendering Threads

[Gary Kleiner]

It shouldn’t make a difference for you. Did you time it, or did it just ‘feel’ different?

[Jim Prisby]

Gary,
I didn’t time it but it made a noticeable difference of 2 to 3 times faster. I’m just not positive this was the only thing that changed at the time. My computer may have been processing slower for some other reason that was corrected by my maintenance updates. That’s why I was asking about whether this was logical. Is this setting related to the number of threads your processor can process at one time? I don’t fully understand the relationship here. Can you explain in more detail?

[Terje A. bergesen]

The number is the max number of operating system threads Vegas will start to render your video. Threads are difficult beasts, but they can significantly speed up any application. Even on a single CPU, no dual core, no hyperthreading, multiple threads can have a significantly positive effect on application performance. The reason for this is that most applications spend most of their time waiting for something, not doing any processing. Splitting the app into multiple threads will create better utilization of the CPU, even on a single CPU system.

How about rendering software? Well, rendering is mainly a CPU-bound process. Data is moved in and out of memory and a small (compared to the overall work) amount of disk reading and writing is taking place. Rendering therefore sees a far better improvement in speed on multiple CPUs than the typical application.

This may also actually mean that having too many threads doing CPU-bound rendering running on a single CPU may actually negatively impact performance. The reason is simple. THe process of scheduling threads, moving data in and out of memory for them, etc, takes some of the CPU cycles. If there are too many threads, the scheduling of threads (as opposed to actually running them) may consume most of your CPU cycles. This is not going to happen with only 4 threads, though.

So, I would say that there is a good chance your observations are accurate, having 4 threads may slow down your rendering. There is only one way to find out, and it isn’t really that hard. Create a project, save it. Reboot your computer. Start Vegas. Start rendering. Time it. Change the thread parameter. Reboot your computer. Start Vegas. Start Rendering. Time it. Repeat a few times for accuracy.

The reboot of your PC is so that each render starts with the same parameters. If you do this test after running 1 or 2 apps or doing other stuff, you will not get good data.

—
Terje A. Bergesen

[Jim Prisby]

Sorry for the slow response, Terje. Thanks for the very detailed information. I really appreciate it. I’m sure others will benefit from it as well. I will do the test as you suggested.