Embree & ForestPack = massive render slowdown?

[TheRazorsEdge]

I've done a quick search and didn't find anything really related, so I'm posting this here.

I noticed a massive render slowdown when shifting a scene with Forest Pack 4.40 and a good number of VrayProxies for trees etc from Max 2014, Vray 2.50.1 over to Max2015 SP3 Vray 3.2.03.

Here are the Rendertimes:

Max2015 SP3 Vray 3.2.03 Embree enabled: ~25min/Frame; LC: ~14 min

Max2015 SP3 Vray 3.2.03 Embree disabled: ~4min/Frame; LC: ~2 min (still a really nice speed-up over Vray 2.5)

For comparison:
Max 2014, Vray 2.50.1: 6.30min/frame: LC:2.45min

This is for a fly-by animation of a pretty detailed stylized forest scene, btw. In terms of render settings, nothing changed from Max 2014, Vray 2.50.1 to Max2015 SP3 Vray 3.2.03, except that Embree is enabled by default in Vray3, so I was fairly quickly able to pinpoint it to "Embree" being enabled or disabled. Not sure if this really has to do anything with Forest Pack, but maybe with the VrayProxies? Has anyone else noticed anything similar?

Cheers!

[vlado]

How many cores do you have in your machine? Also how many different trees? Embree has a severe problem with poor multithreaded memory allocation when building its acceleration structures (and this is a process that needs to be done when the proxy is loaded during rendering), although it is typically a lot faster for raytracing. Normally it's not a big issue, but it shows up in some scenes. We still haven't gotten to rewriting that part of Embree.

Finally, Forest Pack needs to be recompiled to take advantage of the proxy speed up improvements in V-Ray 3.20.03 specifically - not sure if they guys at Itoo managed to do that.

If you still have issues, it would be best to take a look at the scene.

Best regards,
Vlado

[TheRazorsEdge]

Hi Vlado,

thank you for the speedy response and the info.

The machine in question is a Core i7-3820 (4 cores 8 threads) and there are, I'd say about 10 different high-res trees and bushes as Vrayproxies plus some more high-res plants as EditableMesh. I don't know how many Forest instances are placed in the scene, if that's what you mean, but there are quite a few.

Now that I found out about it, it's not much of an issue, only faster would obviously be nicer.

The other thing I found is, that for the scene to render faster, not only do I need to uncheck Embree, I need to kick off a render, cancel it, check Embree (or have it left checked), then uncheck it again. Now the scene renders with the above faster times, it starts out slow both for the LC and then the render, even with Embree initially unchecked. Canceling and doing the above, speeds it up. It's slow initially regardless of what the check-box says.

I'll check the Itoo Forum later for some info there as well.

Cheers!

[vlado]

It's slow initially regardless of what the check-box says.

Could it be because Windows caches the proxy files that you are using the first time you render the scene? And not specifically about Embree?

Best regards,
Vlado

[AndresAhumada]

i have issue too.

Some times the render crush...

[vlado]

Some times the render crush...

It's generally better to start new threads about your issues. Nine times out of ten in these cases the issues are different and it's very confusing to track who is having problems with what.

With that said, can you send any crash dumps from CER to vlado@chaosgroup.com so that we can look into them.

Best regards,
Vlado

[TheRazorsEdge]

Thanks again for the speedy reply.

Not sure about windows caching the proxies being the problem or not. All I can tell is that if I leave the initial render running, the LightCache calculation, the first and and every successive frame take "forever" to render unless I cancel and do what I described to start another render. I don't have to wait for the first calculations to finish, btw. I just kick off a render, cancel it, do as described and then the render is proceeding a lot faster.

Cheers!

PS: Totally unrelated, but I just yesterday realized that you guys introduced "render specific frames" in the latest Vray for Maya. That's absolute gold! Thanks a lot.

[im.thatoneguy]

I did some testing here on one of our really heavy forestpack scenes (several billion trees about 100 million unique polies of instances). No difference w/ and w/o embree both on 40 thread Xeons or 12 thread i7s.

On the i7 (3930k) it was about 57 minutes and 60 minutes. Well within the margin of error for random variation of renders. We are seeing oddities like some frames rendering 3x faster on the dual Xeon 2560s and sometimes they render the same across not only our 12 thread i7s but also our 8 thread older i7s.

[vlado]

We are seeing oddities like some frames rendering 3x faster on the dual Xeon 2560s and sometimes they render the same across not only our 12 thread i7s but also our 8 thread older i7s.

I would suggest trying the new build of ForestPro that is built against the V-Ray 3.20 SDK, whenever that becomes available. It should improve some of that.

Best regards,
Vlado

[vlado]

Ah, and make sure that the bitmap pager is OFF in 3ds Max

Best regards,
Vlado