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zanny

Member

From: Baltimore

Registered: 2012-10-05

Posts: 84

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Do modern IGPs under Mesa actually use allocated video memory?

I have two systems - one with Intel 4600, and one with AMD 7660D graphics. I've been mucking around all day trying to figure out if the Mesa drivers (in this case, r600g and i915) actually use video RAM you dedicate to the IGP in firmware.

I can't quite figure it out, though. I don't really get any OOM errors, and I've used the scientifically reliable young brother method on both systems while he played Minecraft, and he reports infrequent freezing I'd associate with some internalized GC happening more often only on the AMD system when I had the gpu memory under 128MB.

Otherwise, I've had my 4600 system at 32MB (the minimum in the bios) for months, without any negative impact. The AMD system seems to have some means to use that memory, but the Intel part doesn't do it at all. And google-fu this afternoon has lead me no where, and searching the mailing lists on xorg doesn't turn up anything either.

So does anyone know if, and to what degree, the Intel / AMD GPUs actually use preallocated video memory, in concrete terms? Or just know any Mesa resources that answer the question? Right now I have the AMD system at 256MB and the Intel one at 32, and the Intel system can play Metro Last Light just fine at ~40 fps on low settings. I've been trying to get PTS running on the AMD system for a while, but I have OpenSuse on it (I sinned, and I paid the price) because the official repo version of PTS is only at version 4.2, and manually getting all the updated packages for 5.0 is being a real PITA without delicious pkgbuilds.

Last edited by zanny (2014-04-19 18:24:33)

Gusar

Member

Registered: 2009-08-25

Posts: 3,605

Re: Do modern IGPs under Mesa actually use allocated video memory?

It depends on what you're actually setting in the firmware - the framebuffer or whole video ram?

On my Intel machine, I have two settings - "Internal Graphics Memory Size", which I think is the framebuffer; and DVMT ("Dynamic Video Memory Technology"). The first one I've set to 32MB, the second to "max". So 32MB is permanently reserved for the GPU, the rest is allocated dynamically by the OS (btw, the memory manager is in the kernel, not in Mesa) to the maximum extent possible.

Not sure how that's handled on AMD machines, but it seems to me the setting is for the whole video ram, the equivalent of DVMT. In this case, memory is still allocated dynamically, but never more than what you've set it to.

Last edited by Gusar (2014-04-19 19:25:39)