Does anyone else also have experienced slower simulations on TOPs in relation to a normal ROP geometry? Most of my simulations are much slower on TOPs kind more than double, I am missing something?

I am on Linux with houdini 18 build 416.

Thanks.

There are a few things to consider:

• Make sure All Frames in one Batch is enabled on your ROP Geometry if you're running a simulation, otherwise each work item will be run individually and the jobs will collectively do an N^2 amount of work.
  
• ROP Geometry work items in TOPs cook out of process. If you work items are only doing < 2s worth of work each, then you'll spend most of the time spawning processes. Even if you're writing sim source caches which don't need to write sequentially, you probably want to set Frames to Batch to something larger than 1 if the per frame workload is small.
  
• Because the work items cook out of process, they're starting from a freshly loaded copy of the .hip file with no existing caches. If you've already cooked part of the sim in your Houdini session with the viewport, using a regular Geometry ROP may just write out that cached data to disk. For a fair comparison, you'll need to compare TOPs to a fresh Houdini session that has not yet cooked any of the sim data (e.g. load the .hip in manual mode)
  

There will be overheard from running out of process, but it should be quite small. For example, in the $HH/houdini/pdg/examples/top_rop/rop.hp example file the smoke_sim node takes 1:09 to cook directly using the underlying Geometry ROP and 1:13 seconds when cooked through TOPs.

If you have a file the demonstrates the issues you're having we'd be happy to take a look.

I think that the real benefits of caching geometry on TOPs in this situation can only be obtained using a render farm, when on a farm we can have much more machines than processor cores.

tpetrick
There are a few things to consider:

• Make sure All Frames in one Batch is enabled on your ROP Geometry if you're running a simulation, otherwise each work item will be run individually and the jobs will collectively do an N^2 amount of work.
  
• ROP Geometry work items in TOPs cook out of process. If you work items are only doing < 2s worth of work each, then you'll spend most of the time spawning processes. Even if you're writing sim source caches which don't need to write sequentially, you probably want to set Frames to Batch to something larger than 1 if the per frame workload is small.
  
• Because the work items cook out of process, they're starting from a freshly loaded copy of the .hip file with no existing caches. If you've already cooked part of the sim in your Houdini session with the viewport, using a regular Geometry ROP may just write out that cached data to disk. For a fair comparison, you'll need to compare TOPs to a fresh Houdini session that has not yet cooked any of the sim data (e.g. load the .hip in manual mode)
  

There will be overheard from running out of process, but it should be quite small. For example, in the $HH/houdini/pdg/examples/top_rop/rop.hp example file the smoke_sim node takes 1:09 to cook directly using the underlying Geometry ROP and 1:13 seconds when cooked through TOPs.

If you have a file the demonstrates the issues you're having we'd be happy to take a look.

Thanks for the feedback I'll take a look on those tips.

I am starting to get used to use TOPs to simulate wedges instead of using normal ROPs because I have the advantage of automation, for a heavy flip sim for instance where I have several process like:

1-Simulate the particles sim and wedges
2-Make the surface cache and wedges for the appearance
3-Simulate whitewater particles and wedges
4-Make the volume cache and wedges for the appearance
For just then to see how the simulation really looks like for render.

And between those a lot of adjustments for a particular scene so TOPs help me a lot but for some cases the sims are much slower like 3-4X times and I am trying to find out why and how to avod that.

In my actual case I am on where I have a much simple Vellum simulation. Where each sim in a ROP SOP takes around 1 min to sim 70 frames in TOPS is taking 3-4 times longer and sometimes it really is the same speed I couldn't figure out why is that. I already try to mess with the scheduler options but so far not a clue.

Anyway thanks again for the tips if I figure out what's going on I'll drop by.

Cheers!