Setting the number of Light Cache passes higher than the number of threads

[andy_butler_7]

Hi all.

We have one machine which has 24 cores. 6 quad core CPU's to be precise with hyper-threading on. When we are preview rendering locally we set it up to have 24 passes in the Light Cache to get the extra speed from the machine.

My question is, if we send a job to the network and have this set on 24, if a machine with a lower number of CPU's picks the job up, does it have an effect on render time? For instance will a machine with 8 cores, try and do 24 passes or does it only do 8? Therefore making it really slow to do the Light cache calculation?

It would be so handy to loose this feature and just have it built in to Vray to use however many cores the machine has. Or maybe putting it on 0 would make it Auto and any other number would force it to use that number or cores or something along those lines.

What are your thoughts on this?

Cheers.

Andy.

[vlado]

My question is, if we send a job to the network and have this set on 24, if a machine with a lower number of CPU's picks the job up, does it have an effect on render time? For instance will a machine with 8 cores, try and do 24 passes or does it only do 8? Therefore making it really slow to do the Light cache calculation?

It will be fine.

Best regards,
Vlado

[vlado]

It would be so handy to loose this feature and just have it built in to Vray to use however many cores the machine has.

This could lead to differences between the light caches computed on different machines with different number of cores.

Or maybe putting it on 0 would make it Auto and any other number would force it to use that number or cores

This is already done since a while now in the latest service packs.

Best regards,
Vlado

[muoto]

Huh, just out of curiosity, what brand of computer has 6 quad core cpu's ?

[super gnu]

i suspect he means 2 6-core cpus (hence 4 6-core cpus if you include hyperthreading) ive never heard of a 6 cpu motherboard and even if one existed, 6 quad cores with hyperthreading would be 48 threads not 24.

[muoto]

Ok,
btw, i never realised hyptertheading was turned of my my dual quad core workstation.
Will it go faster when turning on ?

[Morne]

Ok,
btw, i never realised hyptertheading was turned of my my dual quad core workstation.
Will it go faster when turning on ?

yes
about 20 to 40% faster

BUT, are you sure its turned off? It's ON by default on Intel
AMD doesnt have hyperthreading

[muoto]

It was indeed OFF (dell workstation), just turned it ON, and have now twice more buckets woow nice to see all these small buckets rendering
I will check on my other workstations, and will for sure check on my new one that's coming next week.

[Morbid Angel]

I would caution about usage of HT. In our recent setups, HT has actually affected the rendering in a negative way. When you deal with so many threads there can be redundancy. Some of that was vray specific problems which were solved (I hope). Our tests showed we only had about 10%-15% gain with HT on.

[vlado]

In our recent setups, HT has actually affected the rendering in a negative way.

Yes, however those were somewhat specific situations; in the general case there is a definite improvement with HT.

Best regards,
Vlado

[andy_butler_7]

This could lead to differences between the light caches computed on different machines with different number of cores.

This is already done since a while now in the latest service packs.

Best regards,
Vlado

Thanks for all your replies Vlado. Regarding the 0 already being available in the latest service packs, is that only with Vray 2? We are using 1.5 SP5 still.

[andy_butler_7]

Huh, just out of curiosity, what brand of computer has 6 quad core cpu's ?

Ha ha. Good point. It actually has 4 cpu's with 6 cores. Hence 24..... Small typo before! Whoops!

[vlado]

Thanks for all your replies Vlado. Regarding the 0 already being available in the latest service packs, is that only with Vray 2? We are using 1.5 SP5 still.

Yes, this is in V-Ray 2.0

Best regards,
Vlado

[trick]

Ha ha. Good point. It actually has 4 cpu's with 6 cores. Hence 24..... Small typo before! Whoops!

Let's try again: 2 cpu's with 6 cores and hyperthreading is 24 threads. Or 4 cpu's with 6 cores and hyperthreading is 48 threads ?

[andy_butler_7]

Let's try again: 2 cpu's with 6 cores and hyperthreading is 24 threads. Or 4 cpu's with 6 cores and hyperthreading is 48 threads ?

Trick, you don't miss a trick do you!! I clearly had a poor knowledge about hyperthreading and cores etc..... Just cleared it up with he in the know. It has 2cpu's with 6 cores and hyperthreading. Hence 24 cores. Thanks for teaching me a lesson!

Regards

Andy.