GPU acceleration - How much CPU is required?

Hulk wrote on 12/17/2011, 5:18 PM
Now that Vegas has GPU acceleration, and it seems to be quite powerful from what I'm reading, I'm wondering how much CPU power is really necessary for Vegas? Now I realize that a computer is used for more than Vegas but honestly a dual core 2100 (4 cores with hyperthreading) is a very capable CPU for image editing and other applications.

Even assuming a 2100 is not powerful enough, how about a 2500k quad? How much CPU is necessary in Vegas with a good GPU?

I would love for someone with a fast system and a good GPU to disable some cores, or lower the multiplier to reduce CPU performance and see what that does for GPU performance. It's pretty easy for anyone with a "k" series CPU to lower to the multiplier to 20 or so.

- Mark

Comments

NicolSD wrote on 12/17/2011, 5:33 PM
It all depends on what is acceptable to you. It varies from person to person. I have an old Core 2 Duo with a new GTX 570. Rendering is now almost at an acceptable speed but trying to preview anything is horrible. That is why I am saving my money for a new CPU (I have already bought the new mobo for it).

But I am not going for the slowest CPU I can get away with. After 20 years of building computers, I can tell you that it is never the way to go. You should always go for the best, most powerful CPU you can afford. Not the best, most powerful CPU on the market but the best you can afford. Usually, I try to save a couple of months longer so that I can get something even better than I should really buy.

I bought hundreds of computers over my 20 years and I firmly believe in this principle.
MPM wrote on 12/17/2011, 6:17 PM
>"Now that Vegas has GPU acceleration, and it seems to be quite powerful from what I'm reading, I'm wondering how much CPU power is really necessary for Vegas?"
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Things aren't that neat & tidy. :-)

Working with audio/video you're reading a stream of data, manipulating it for display in Vegas or whatever app, maybe shoving that data through one or more processes including encoding, & writing the results to another stream & that probably to disk.

You need to read the incoming data streams fast -- the entire process is going nowhere if it's starved of data to work with or on, & the same goes for writing to disk. When it comes to viewing the data in Vegas, i.e. video on the timeline, your graphics hardware, other video software, version of windows, & the format of that video all have effect. For processing/encoding that data add effects from the brand/model of CPU, motherboard, & RAM to the relative efficiency of the code in both Vegas & whatever encoder. For a lot of stuff an i7 on the right board is going to be much faster than an AMD running at the same speed. When it comes to cores, visualize a 2 lane highway branching out to 4-8 lanes & back to two -- since you've got the constriction of 2 lanes before & after, those extra lanes cannot have maximum effect. When you try to divide video processing across 4 or more cores, Plus send data back & forth to the GPU, it's hard to keep everything nicely timed & moving forward. Extra power's there -- it's just very hard to use all of it.

So anyway, trying to answer your question, "how much is enough"?... Depends. :-)

If you're reading smaller files or a lower bandwidth incoming stream, you don't need the fastest SSDs. If you're putting 320 x 240 video on the timeline rather than 1080p, the most expensive graphics cards will be of little help. If you're not doing a lot of processing, say Not going from 1080p to 480i or 320 x 240, code efficiency isn't as important. And if you're encoding mpg2 or mjpeg avi, you can in my experience easily get by with surprisingly little CPU horsepower [using ATI mpg2 hardware encoding, CPU load with a P4 single core was only ~12%]. If you're not previewing a lot of FX, RAM can be less important too -- with a multi-boot rig, encoding the same project in XP Pro 32 vs win7 64 with 6 GB RAM [~3 GB of which is available in XP], sometimes XP is faster.

Like anything audio/video, my advice would be to start at the end & work backwards, from finish to start, figuring out what's most important along the way. Then budget accordingly. If you're doing HD, it's going to take a certain amount of GPU just to easily display it, & a certain amount of HDD space & speed to handle the files. Figure out your graphics hardware & you've figured out how big the power supply has to be. Then take what's left, figure out what you can afford, & start researching performance.
Hulk wrote on 12/17/2011, 9:22 PM
You can forget about hard drive's being a bottleneck with modern computer systems unless you are editing multiple streams of uncompressed 4:4:4 HD. I ran a video editing benchmark site for years and even with the slower drives of 5 years ago hard drives weren't the bottleneck. It is CPU and now GPU with Vegas.

As for "enough" I'm referring to the point where Vegas with GPU acceleration fails to show significant performance gains.

We can theorize all we want but until we see some actual testing no one knows.

Like I said let's see someone downclock their 2500 or 2600 to 2GHz or so with a powerful GPU and see how preview and rendering is affected?

- Mark