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GPU vs CPU
I was reading through some previous posts and I want to confirm something.
I have recently upgraded my kit and one item that came with my prebuilt machine was a GT640M card.
I previously had a i950 GTX 260 and I now have a i3770s with the GT640M.The rendering times have halved between the machines, but when I try to tweak the CUDA vs CPU on the new machine, I get little / no difference in rendering times.
Is this expected behaviour?
John
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6 Replies
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Just been running my own tests using the preview window setttings and testing HD4000 against the OpenCL / CUDA and CPU only.
Preview of a 3D HD (5.1) video (side by side) using CPU or HD4000 gives no more than one FPS.
Using the OpenCL / CUDA cores gives 10 FPS (ten times better!).
I have an SSD arriving tomorrow and an extra chunk of RAM – I will see how that improves things (if at all).
My original questions (regarding rendering) still stands – but the preview window test proves that the software is using the OpenCL cores for preview at least…
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Your conclusion is pretty much correct. Your video card will help with the preview a bit but it will be hard pressed to give any support to your i3770 during rendering. Your render times being halved are completely due to your processor upgrade. The GT640m is a fairly capable card outside of video editing but it is a second tier card and 10 fps in the preview is what you will average with second tier cards. The “X” cards are far better for getting your video preview up to 24 or 30 fps except the fact that your previous gtx 260 card was a bit old and the 640 despite its architecture limitations is newer and compensates a little for that lack of the “X” factor. With an i3770 a gtx 460 will probably let your reach 24 fps or higher. Anything less (that is budget cards that are less than about $160 US) will struggle to keep the preview running in real time and will do very little to get better AVC rendering times. With newer gtx first tier cards you would probably see about a ten percent (maybe less) performance boost in rendering coupled with the i3770.
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I did a render test with my new system (Intel i5 3.4Ghz and ATI Radeon HD7850 graphics card). I did one render with GPU render selected and a second render with CPU only selected) and the render times were pretty much equal. Maybe there was a 4 second difference between them, with total render time taking 4 minutes.
I may be wrong, but it seems to me that if you have an older (ie- slower) processor and a newer, high-powered graphics card, then the render times will be shorter if GPU render is selected.
Dave
Intel i5 3570K Ivy Bridge 3.40GHz quad core
Asus P8Z77V-LK
16gb RAM
ATI Radeon HD7850 2gb
Crucial M4 SSD + Seagate Barricuda 7200rpm
Windows 7 Pro 64 -
[John Kendrick] “I have recently upgraded my kit and one item that came with my prebuilt machine was a GT640M card.
I previously had a i950 GTX 260 and I now have a i3770s with the GT640M.”I assume you mean you had an i7-950 and now you have an i7-3770? Based on a handy benchmark, the i7-3770 does a 9642 average CPU Mark, while the i7-950 does a 5717. So, ok, that’s a 1.69x improvement on generic stuff.. and if there’s any Ivy Bridge optimizations in the video CODECs (or things that just optimize well), you might well see a 2x improvement just based on the CPU.
What version of Vegas are you using. Since you said “CUDA”, I’m thinking maybe 9 or 10? Earlier versions of Vegas with GPU acceleration didn’t do all that much acceleration. Part of that was that the GPU can only do so much if the CPU is the weakest link, prior to Vegas 11, only the CODEC could be accelerated (well, not entirely true… some plug-ins used OpenGL). If you’re using Vegas 11 or 12, you need to enable OpenCL in the options panel.. it’s not a per-CODEC setting anymore.
But also, consider the difference between CPU and GPU. The CPU is fairly easy to program, very general purpose, used in a straight forward way. For rendering, it’s also fairly simply to make things scale to multiple threads, so each CPU core can be kept busy. But you only have four cores.
The GPU, on the other hand, is a very specialized processor, kind of hard to program, and made up of hundreds or even thousands of processing elements. OpenCL (or, previously, CUDA) made this eaiser, but it’s still in a sense fitting the problem in a special way. And there are delays — the problem has to be compiled for the GPU, sent to the GPU, received by the processors, etc. So it gets very complicated to make a program like Vegas use both your CPU and your GPU very efficiently.
The bottom line is that, as your CPU increases in performance relative to the GPU, and also compared to the fairly fixed delays in processing data for the GPU, you find the GPU helps less and less. When I did my experiments with Vegas 11, I had a six core AMD processor, and used both nVidia and AMD processor cards (both cost around $300 each, so it was a price-based comparison). I found that with both cards, my usual 90-95% CPU utilization fell to around 80%. The nVidia card reported 60-80% use, the AMD reported around 50% use.. and yet, things rendered faster on the AMD. Hard to say just why.. different architectures, and I suppose AMD might have been ahead of nVidia on OpenCL optimization. Both helped me.. but you have a much faster CPU.
So do check the settings, don’t worry about GPU unless you have Vegas 11 or 12, least as far as Vegas goes (might be useful with other tools), and don’t worry too much if the GPU doesn’t help on everything. It will probably help out more on some plug-ins than any general rendering, anyway.
-Dave
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Vegas Pro 12 is the software.
Keen to understand then, should I use the OpenCL rather than CUDA rendering? When i select “Test my GPU” it only shows the CUDA option, not the OpenCL.
You are right, the old machine was the 950, the new one is teh 3770S
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Make sure you have the latest graphics drivers. nVidia has lagged a bit in OpenCL support, primarily because they were concentrating on their proprietary CUDA system instead. At least in Vegas 11, I tested a GTX570 card under CUDA, and it worked fine in Vegas (actually failed on a few OpenCL benchmarks). But Vegas 11 didn’t have a global CUDA option (eg, Preferences/Video/GPU acceleration of video processing) — didn’t realize Vegas 12 did (I have an AMD card in my system).
-Dave
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