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Graphics Cards

Journeyman III

How exactly is the VRAM allocated in APUs


I'm a newbie Linux Enthusiast, interested in Radeon Vega Integrated GPUs. I wanted to know what piece of code reserves the amount of VRAM from DRAM in APUs. The usable RAM on both Windows and Linux shows up as 1gb less of the total DRAM that I have, (yes, I know it's reserved for the VRAM), I wanted to know how exactly is it allocated. In kernel documentation, they say it's carved out by the BIOS. Now I want to know how exactly is this BIOS region accessed by the driver and reserved the required memory. 

Is the driver using kmalloc to allocate the memory? Any replies would be greatly appreciated!

3 Replies

To increase or decrease your PC APU's vRAM  you need to go into BIOS settings and locate the IGPU settings. Most settings has a maximum of 2 GB of vRAM you can assign to your APU graphics. Possibly with the newer BIOS versions this amount might be higher now.

If you have a laptop, that option may not be available and you are stuck with whatever vRAM is default for your laptop. Some laptop's you can change the vRAM amount for your APU.

I don't believe that any OS can change this BIOS setting so you need to look in your BIOS for your motherboard and find everything concerning IGPU or Graphics and see which setting is the one that can increase or decrease your vRAM for your APU.


Hi, thanks for your reply, but I'm not looking to increase or decrease VRAM. I;m tryng to understand how exactly is the system driver reserving VRAM from RAM. More to the technical side, I'm leaning towards the programming side of the Linux Driver. What section of the BIOS (Memory region or the instruction set) is being read by the Driver? I'm really unsure if I asked in the right forum section.


You might want to ask your question on the developers part of the forums. Probably lots there that could answer your question.