APU/iGPU VRAM Limit

[PC HEROES]

Hello all....

 

I know that back when the Vega Integrated Graphics came out and even before Ryzen was available we were limited to only 2GB of VRAM that came from the System RAM. So if you had a 16GB Kit and were using Integrated Graphics it would lower your System RAM to 14GB.

 

I was wondering if this has changed and the limit has increased? It would be nice if we could increase it to 8GB for a Lower End eSports/Emulation PC.

[porina]

If I enable the iGPU on my 5800H (Zen 3) that by default reserves 2GB of system ram. The bios allows me to reduce it but recommends against it. I found the best option was to disable it totally and stick to dGPU.

 

Anyway, there wouldn't really be much point in reserving more for it. I think the 2GB is for the driver/hardware to know there will always be that available. If needs increase beyond that, it will dynamically take it out of the rest of the system pool.

 

On a dGPU hitting system ram as overflow is bad because of how slow it is. On iGPU it is the same ram so the same performance. Increasing it doesn't change that.

[Eigenvektor]

1 minute ago, porina said:

On a dGPU hitting system ram as overflow is bad because of how slow it is. On iGPU it is the same ram so the same performance. Increasing it doesn't change that.

Exactly. Spilling over into system memory is bad for a dGPU because of the added latency and lower bandwidth. But an iGPU's VRAM is always the same as system memory, so there's no additional penalty. Permanently reserving more than 2 GB would effectively be a waste for any task that doesn't need it.

[Alex Atkin UK]

10 minutes ago, porina said:

I think the 2GB is for the driver/hardware to know there will always be that available. If needs increase beyond that, it will dynamically take it out of the rest of the system pool.

My guess is the reservation is two fold:

1) ensures there is a large block of unfragmented RAM always available

2) as its reserved, you wont run into issues of the OS constantly trying to free enough RAM for a slight increase in VRAM usage.

 

The idea is the reservation is enough that the majority of the time, there is enough to avoid stalls from the OS trying to free up more.

 

As such yes, it has increased.  Its a known tweak on the Steam Deck to increase its reservation to 4GB if you play a lot of games that need that much VRAM.

 

3 minutes ago, Eigenvektor said:

Exactly. Spilling over into system memory is bad for a dGPU because of the added latency and lower bandwidth. But an iGPU's VRAM is always the same as system memory, so there's no additional penalty. Permanently reserving more than 2 GB would effectively be a waste for any task that doesn't need it.

There IS a penalty if you have no free RAM at the time it needs more.  Thus why the reservation can be changed based on your usage to mitigate this.  But as most iGPUs are just for desktop use, its defaulted to what is expected to be needed for the frame buffer alone.

[Eigenvektor]

13 minutes ago, Alex Atkin UK said:

Well there IS a penalty, if you have no free RAM at the time it needs more.  Thus why the reservation can be changed based on your usage to mitigate this.  But as most iGPUs are just for desktop use, its defaulted to what is expected to be needed for the frame buffer alone.

Sure, if the iGPU needs more memory and none is currently available, that is bad. But so is permanently reserving a large chunk of memory when it might be more useful as system RAM. Either situation would be solved by increasing the total amount of RAM. Or simply buying a discrete GPU (which is generally more cost effective in terms of perf/$)

 

~edit: let me put it another way: if the iGPU needs more memory and none is available, that means the total memory requirements exceed what is available. Reserving more memory for the iGPU will likely simply reverse the issue. iGPU happy, CPU task out of memory instead.

[Alex Atkin UK]

14 minutes ago, Eigenvektor said:

Sure, if the iGPU needs more memory and none is currently available, that is bad. But so is permanently reserving a large chunk of memory when it might be more useful as system RAM.

Which is why its only something you really should think about if you're gaming on an iGPU.  A slight stall as your VRAM consumption goes up is likely not going to be obvious in desktop use, but in gaming it would be a complete mess, especially given in games the VRAM usage likely will be changing constantly.

 

I just checked two machines, one Linux one Windows, and it seems with a 4K monitor and loaded up with software they both are using 2GB+.  With less software open it drops below 2GB, so as you point out the default makes a lot of sense.  It would make zero sense wasting nearly 2GB of RAM when 99% of the time you're only using slightly over the reservation and that stall from reallocating VRAM will probably be happening as you launch the software, where you wouldn't notice as its already reallocating RAM for the software anyway.

 

NOTE: I measured the VRAM on my NVIDIA dGPU as output by nvidia-smi as its the easiest way to actually figure out how much VRAM is being used.  In principle it would be similar numbers with an iGPU just far more relevant due to above.

[Eigenvektor]

3 minutes ago, Alex Atkin UK said:

It would make zero sense wasting nearly 2GB of RAM when 99% of the time you're only using slightly over the reservation.

I was thinking more in terms of permanently reserving 8 GB as OP was asking. On a 32 GB system you might be fine with that, 24 GB is still plenty for a lot of tasks. But if you go with 16, permanently losing half your available RAM isn't a great idea.

 

For a system dedicated to gaming like a Steam Deck that might be fine, but if you do other tasks that may be memory intensive you'd probably end up adjusting the limit constantly.

 

Unless space is at an absolute premium like in a handheld, I'd generally avoid the headache and get a discrete card.

[PC HEROES]

2 hours ago, Eigenvektor said:

I was thinking more in terms of permanently reserving 8 GB as OP was asking. On a 32 GB system you might be fine with that, 24 GB is still plenty for a lot of tasks. But if you go with 16, permanently losing half your available RAM isn't a great idea.

 

For a system dedicated to gaming like a Steam Deck that might be fine, but if you do other tasks that may be memory intensive you'd probably end up adjusting the limit constantly.

 

Unless space is at an absolute premium like in a handheld, I'd generally avoid the headache and get a discrete card.

I was only using 16GB as an example. All I need to know is if it is possible to reserve more than 2GB for the iGPU? A very simple Yes or No will do just fine. I applaud @Eigenvektor for his willingness to see past the negative aspects of this, it is a lot cheaper to buy more RAM than it is to get a Dedicated GPU.

[Alex Atkin UK]

4 hours ago, Eigenvektor said:

I was thinking more in terms of permanently reserving 8 GB as OP was asking. On a 32 GB system you might be fine with that, 24 GB is still plenty for a lot of tasks. But if you go with 16, permanently losing half your available RAM isn't a great idea.

 

For a system dedicated to gaming like a Steam Deck that might be fine, but if you do other tasks that may be memory intensive you'd probably end up adjusting the limit constantly.

 

Unless space is at an absolute premium like in a handheld, I'd generally avoid the headache and get a discrete card.

Even Steam Deck won't let you set it above 4GB.  Makes sense, as gaming at 800p on a small screen, you don't need high resolution assets.  The catch is a few games not scaling as low as they could.

 

2 hours ago, PC HEROES said:

I was only using 16GB as an example. All I need to know is if it is possible to reserve more than 2GB for the iGPU? A very simple Yes or No will do just fine. I applaud @Eigenvektor for his willingness to see past the negative aspects of this, it is a lot cheaper to buy more RAM than it is to get a Dedicated GPU.

I think the point is you only need to reserve the RAM when you have limited RAM, so its not having to fight the CPU for resources.  If you have plenty of RAM the issues it solves are likely null and void, so you don't need to make it bigger then as it will dynamically expand as required.

[Eigenvektor]

6 hours ago, PC HEROES said:

it is a lot cheaper to buy more RAM than it is to get a Dedicated GPU.

If reviews are to be believed, an R7 8700G costs around the same as an i3-12100F + RX 6600. The i3 + dGPU will give you roughly double the performance at the same price.

 

https://www.youtube.com/watch?v=Ye60Wf8lUt8&t=914s

 

Of course there are cheaper CPUs with iGPUs, but my point is: check reviews before you decide to jump on it. There may be a cheap(er) dGPU + CPU combo out there that outperforms it.