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titan memory split
Posted: Sun Jan 10, 2016 4:29 pm
by stoiqa
I have a titan 6gb, and two 780 ti's
When titan is single activated and priority. it shows 6gb in toggle info,
I leave it in priority, and activate the other two without priority, and it splits my vram to 3gb.
is the slot order important, or.. (ti's are in the first slots, and titan in slot 4)
Re: titan memory split
Posted: Sun Jan 10, 2016 4:47 pm
by brasco
CUDA can only allocate the RAM equal to that of the lowest card, so it's taking the 3GB of the 780 Ti as the maximum.
If you run just the Titan, you'll have access to the 6GB.
cheers
brasc
Re: titan memory split
Posted: Sun Jan 10, 2016 5:18 pm
by stoiqa
that's interesting, so if I have two titans and one 780 ti, is still gonna take 3gb,
Not really making sense, should be able to set priority of one card and use the bigger memory...what's the point of priority then?
Re: titan memory split
Posted: Sun Jan 10, 2016 5:58 pm
by brasco
Priority has nothing to do with Memory.
It's to do with how much the card will be utilised for CUDA tasks, so if it's set to High, the GPUs will work at max, if you have the display GPU at max it'll become very slow to interact with the machine.
In 3.0, priority may be removed entirely since it was designed to make the system more responsive whilst you where rendering and still interacting with the machine (most relevant if the display card is rendering too) and that seems to have been eased somehow.
Here's what I do if I'm interacting with a scene (Gpu1: is my display GPU):
But overall, this has zero to do with Memory. So yes, if you're loading a scene using all GPUs, CUDA has to mirror the scene in
each card, so the max for that array is 3GB. This may change in the future with shared memory but is currently not possible.
cheers
brasc
Re: titan memory split
Posted: Sun Jan 10, 2016 6:19 pm
by stoiqa
ok, so if I use 2 titans at 6gb, that's 12 gb with a 780ti in the mix ...Ill get 4gb shared?
Re: titan memory split
Posted: Sun Jan 10, 2016 7:08 pm
by brasco
Nope, it can't share any memory so it can't be more than the max of each device:
GTX Titan 6GB
Usable RAM = 6GB
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GTX Titan 6GB
GTX Titan 6GB
Usable RAM = 6GB
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GTX Titan 6GB
GTX Titan 6GB
GTX 780ti 3GB
Usable RAM = 3GB
The RAM does not add up, the limit is set by the individual cards, and therefore it has to go to the lowest card's RAM limit to be able to render the scene.
FYI 3GB is probably fine for most scenarios, are you finding you're running out?
cheers
brasc
Re: titan memory split
Posted: Sun Jan 10, 2016 7:16 pm
by stoiqa
just trying to figure it out, very helpful info, thx
and yes 2 titans and one ti = 3gb
