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Slow rendering with HT Xeon on WinXP
I bought this up before on the old forum but I am having to render some stuff in Afterburn again and wondered if this issue had been resolved?

Basically render times are nearly 3 times longer when Hyper Threading is enabled on a dual processor system with winXP SP2 installed.

An identical machine running windows2003 server renders as expected.

If HT is disabled the machines seem to render as expected but obviously anything else that is rendered with other software can no longer take advantage of the HT.

It is very annoying to have to reset the render farm whenever we need to use Afterburn, I wondered if this issue had been recognised and maybe if it had been fixed in version 3.2a which I can't seem to get access to.

Hello Paul,

Actually you can disable HT if you're using a computer for rendering purposes without the fear that you're loose rendering speed.
Usually with or without HT speed will vary around few percents.

We will redo AfterBurn rendering for next version.


This may be true of Afterburn but our primary renderer is finalRender and when HT is enabled render times are almost halfed in some cases.

The problem is that single cpu systems with HT enabled or disabled there is negligible difference with afterburn but on a dual processor system the difference is massive. For some reason this does not become an issue on win2003 server but does on winXP.

To disable HT is a laboriuos process of going into the bios on each render node. For some reason the suprermicro bios on these machines takes ages to get into and it is not something you want to be doing regularly.

fume fx is looking very good by the way.
That is intersting info I didn't know about fR, that on dual procs with HT it is rendering even faster than without HT.
We will take a look into it.

Thank you

Just to clarify, the speed increase with HT is primarily for fR scenes only, i'm not sure what impact it has on scenes containing Afterburn.
Saying that Final Render is incresed speed due to Ht is not something i can confirm..
Even 2day in Stage1 R2 Alpha s their is still lots of Passes that are Single Threated ( they are getting less and less) ( preparing light , preparing surface scattering from light , Balancing photons , Scattering Objects for 3d motion blur , MTD preparation passes etc..etc..) ..

And as usual when that happend , only 1 and 1 only detected thread on the machine will be allocated and used to process theese render passes .. Alot of stuffs are like that in 3dsmax ( reactor , cloth ( gettingbetterin 9) tec...etc..) so i Highly suggest to turn off Any HT ( witch is really not worth it comparing to a dual core) on systems running max and rendering with stage1 ( or else 3rd party raytracers that i know of for that matter) ..

practical example: having a dual 3.2 Xenon with HT turned on will use 1\4 of the full potential during single threated processes while when turning it off ( bios) allows Half of the full power for the same single threated task ..
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The benefit of HT is scene dependant but in most cases you do see more performance. You are right about the pre-calc stuff being single threaded but if the pre-calc takes 5 minutes and your frame takes an hour to render then surely it is better to have the speed increase over the longest part of the render.

Sure there are instances where HT is not beneficial but with anything that takes over 15minutes and has a quick pre-calc then imo it is definetley worth using.

In an ideal world multiple cpus with multiple cores would be great but you can't just keep going out buying new machines all the time.
i agree with u paul on what ur saying and understand it..

Keep in mind that the most MT part needs to be happening on the Max side and trust me they are doing it tiny bit by tiny bit every releases as i m not alone asking for that on the advisory board from a while now..

As mentioned max9 is a bit better ,and max10 will be as well even more..

Now for third party developers ( kreso , ed , etc..etc..) i think its a pain to MT passes of calculation .. Ull see in Next Products from SitniSati , their is Alot of those improvement MT implemented witch hopefully they will be able to Port to the current AB and Dreamscape plugins ..

Their is Another little point , Voxels and Shader space stuffs are kind of a bit to advance math wize for me ( :roll: ) to speack as an expert about them but one of the last 20 years problemes is the Parallelisism of Differential equations witch basicly can be ruffly translated to " how to MT Task that are Deeply InterDependents within them self " .. and its an actuall big probleme .. anyway its just thoughs that can at least help us understand the 21 century Programmer pain a tiny bit Smile

I m sharing the same vision of an ideal world as urs sir Smile
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