Going to build a new PC. Would like to find the correct forum to ask q’s about RT’s use of CPU cores and GPU use.
Can someone direct me please?
This is the place for questions.
CPU = optimized
GPU = doesn’t use
“Optimized”… Meaning…? Is RT optimized for multiple cores / clock speed? Would I be better off with for example an i5-7500 (built-in graphics) or AMD fx-6300 plus simple graphics card, if one only considers RT as heaviest use.
Optimized meaning it’ll use multiple CPU cores but nothing runs on the GPU.
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Alright, thanks. …still, not sure on best investment fx-6300 vs i5-7500. AMD has more cores. Intel has DDR4 Ram. Intel has much higher single core performance. Decisions, decisions…
Those decisions are always rough! There seem to be plenty of benchmarks on the two, however, wow that AMD chip is cheap! I’d be tempted to spend the $100+ difference on RAM and/or a larger SSD.
I think one of the RT devs, @heckflosse is using an AMD…
Yes, I’m using an old AMD 8-core, the FX8350.
Thanks for the thoughts.
Intel i5-7500 system $725
AMD fx-8350 system $690 (incl $55 vid card)
Includes 16G RAM, SSD drive, “good-enough” mobo, case. (I have a PS, DVD burner, HDD)
Price is pretty much a wash.
Aaaaand… I guess I’ll toss a coin. Ugh.
The AMD FX8350 will eat the saved money be energy consumption in about 1000 hours of usage (german energy prices assumes)
Good point. I did consider that as well, actually. I’m not a die-hard (no pun intended) fan of either make but I’m leaning toward Intel.
I just wanted to make sure I did due diligence in researching and getting enough information regarding RT’s use of CPU power before making a decision.
I hope I will enjoy RT even more with a faster machine.
Thanks all!
Ingo, any idea about how fast with RT are the new AMD Ryzen 5 ?.
Ilias, I can’t tell anything about performance of AMD Ryzen.
What I can tell about AMD (because I use the FX 8350) is, that, especially on Windows, coders have to know about the drawbacks of the 4-way L1-Cache (compared to the 8-way L1-Cache of Intel CPUs) and how to work around them to get max speed from the AMD CPU’s. As I use an AMD for RT and wanted to get max speed also with my AMD CPU for RT you can be quite sure that I did my best to write code which runs fast also on AMD CPUs.
As a note: not taking care of that can lead to 2x-4x increased processing times using AMD CPUs on Windows under special constellations.
Looks like Ryzen’s L1 data-cache is 8-way associative.
@heckflosse, can you elaborate on how cache associativity affects performance? I’m not even super clear on what it is and what the impact is for different algorithms.
Of course: If you have a loop which operates on more than 4 separate channels (each channel being an array in memory) like conversion from RGB to LAB and each channel has it’s own array (not interlaced) e.g something like this:
float *r = malloc(100000);
float *g = malloc(100000);
float *b = malloc(100000);
<fill r, g and b with some data>
float *Ll = malloc(100000);
float *La = malloc(100000);
float *Lb = malloc(100000);
for (int i = 0; i < 100000; ++i) {
LL[i] = some calculation of r[i], g[i] and b[i] will be fine
La[i] = some calculation of r[i], g[i] and b[i] will be fine but throw one of r[i], g[i], b[i], LL[i] out of L1 cache when L1 cache is only 4 way associatve (only on windows, because windows allocates the large arrays to same offset base 4096)
and so on...
}
@CarVacI can explain it more detailed if you like tomorrow 
my current build is a pretty old AMD Phemon ii x4 965 and it works perfectly fine. I think the fx-6300 would be more than enough if you are looking to cut some costs. And like @paperdigits mentioned you could spend the extra cash on ram and and SSD. An SSD makes a huge difference. Did not believe the hype at first but once i got one i do not think i can go back. Good luck
Well, all… I feel quite fortunate. Located a used Acer system in near mint condition. Most important parts; i7-4790, 16G RAM. And for hundreds less than I had budgeted for an i5 new build.
I will add a SSD to the box and I should be good to go after I put a Linux OS on it, with Win7 and Win10 as VM’s. (Currently has Win10 Pro on a 500G spin drive)
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