hyperthreading and big scenes

When you have a big scene you can be tempted to turn on hyper threading, but you rarely see a big improvement in performance.

This is due to a couple of reasons:

The hyper thread pipelines on the same core share the same cache. Because rendering is memory-intensive, hyper threading will increase cache contention, which may degrade performance. Doubling the numbers of threads increases the MR RAM consumption and can cause MR to go into swap, which as we all know will not improve performance

Secondly, multiple threads share the same floating points units so they cannot do arithmetic simultaneously, and since rendering is mostly arithmetic this will affect performance.

Thanks Justin for the tip and clarification!

Comments

[bernie]

I have this problem on a renderfarm which always gives me a cryptic error:

[MUSTER]Process terminated with the following exit code: -1073741819

Which on the autodesk website:
http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=13937915&linkID=9242258&CMP=OTC-RSSSUP01

says I have to disable hyperthreading. AFAIK this is done in the bios which I can't access, but apparently, the magical solution is to use the following pre-render mel:

"threadCount -n 0"

Hope this helps someone.