Why does AMD Vega 8 mobile graphics reserves RAM?

[krkeshav123]

I have a acer aspire 7 with Ryzen 5 3550H, Vega 8 Graphics, 8 GB RAM and a 4 GB GTX 1650 Ti. My usable RAM is only 5.9 GB, which sometimes causes issues while gaming. All of my games use Nvidia GPU, so why is AMD reserving 2 GB RAM. This doesn't happen with its Intel 9th gen counterpart as it has 7.9 GB usable RAM. 

Thank You

[SupaKomputa]

You can set the frame buffer to 512mb instead of auto (2gb preselected).

Go to the bios and find something that says UMA Framebuffer size.

I don't know if this setting available in aspire 7, but i think most gaming laptop should have it.

[porina]

I encountered similar with 5800H + 3070 laptop, however I saw a BIOS setting which allowed the Vega unit to be disabled completely and that freed up the ram it was wasting. Perfect! For a gaming laptop, why wouldn't this be default? It also eliminated the weirdness some software shows when something struggles to choose which GPU does what. In my case the bios had a setting for which GPU was connected to the display. Set it to the 3070 and all was great.

 

I don't know how common this setting is though. My impression is that this is a newer version of Optimus (nvidia + iGPU) allowing this to happen. Older implementations had the display always connected to the iGPU so there isn't a way around it.

[AMD A10-9600P]

8 minutes ago, porina said:

I encountered similar with 5800H + 3070 laptop, however I saw a BIOS setting which allowed the Vega unit to be disabled completely and that freed up the ram it was wasting. Perfect! For a gaming laptop, why wouldn't this be default? It also eliminated the weirdness some software shows when something struggles to choose which GPU does what. In my case the bios had a setting for which GPU was connected to the display. Set it to the 3070 and all was great.

 

I don't know how common this setting is though. My impression is that this is a newer version of Optimus (nvidia + iGPU) allowing this to happen. Older implementations had the display always connected to the iGPU so there isn't a way around it.

They don't disable the iGPU by default because it uses much less power than the dGPU. If you were to use the iGPU on battery you would get much longer run times than using just the dGPU for everything. This is why Optimus exists, on my laptop the dGPU is disabled during lower power tasks and usually on battery, so the lower powered Xe iGPU does the work.

[porina]

14 minutes ago, Benji said:

Because even those don't need to waste more energy than they need to.

 

12 minutes ago, AMD A10-9600P said:

They don't disable the iGPU by default because it uses much less power than the dGPU.

I get why Optimus exists, but my argument was specifically for a gaming laptop, primarily used for gaming. If you want a laptop to run off battery all day doing non-gaming things, that's a different product. If you game at all, it will be plugged in most of the time and power saving is irrelevant.

[AMD A10-9600P]

Just now, porina said:

 

I get why Optimus exists, but my argument was specifically for a gaming laptop, primarily used for gaming. If you want a laptop to run off battery all day doing non-gaming things, that's a different product. If you game at all, it will be plugged in most of the time and power saving is irrelevant.

At the end of the day though it is still a laptop, so it can really serve two uses. It can be used for lower powered work on battery, using the iGPU, and then higher powered gaming plugged in, using the dGPU. Not everyone who buys a gaming laptop is looking purely for plugged in power, they are good options because they flip back between the two use cases, and therefore need to have both an iGPU and a dGPU. Not everyone can buy two machines for their different use cases - I am lucky enough to have a gaming desktop and a thin and light laptop, but for a lot of people that isn't an option, so both of their machines have to fit into one, and it becomes a sort of hybrid.

[porina]

2 minutes ago, AMD A10-9600P said:

At the end of the day though it is still a laptop, so it can really serve two uses. 

I wonder if anyone has done the testing on this on a representative laptop? Just how much benefit does the iGPU give vs fixed to dGPU? I could test it on my laptop but I don't have the time or motivation to set it up in a meaningful way.

[AMD A10-9600P]

Just now, porina said:

I wonder if anyone has done the testing on this on a representative laptop? Just how much benefit does the iGPU give vs fixed to dGPU? I could test it on my laptop but I don't have the time or motivation to set it up in a meaningful way.

I can tell you that even on my laptop with a low powered MX450 dGPU, using the iGPU helps battery runtime hugely. Runtime is massively decreased when the MX450 is being used for a task, so I disable it until I can plug it in. There is a reason that pretty much all gaming laptops (aside from those that sometimes have desktop CPUs) come with iGPUs too, thanks to the fact that they are hybrid devices, made to serve multiple use cases.

[porina]

51 minutes ago, AMD A10-9600P said:

I can tell you that even on my laptop with a low powered MX450 dGPU, using the iGPU helps battery runtime hugely.

I just thought of a test which doesn't involve long running of the laptop. Basically the battery drain rate is reported so that is system power consumption. I used the same display brightness setting for both tests. A USB mouse is connected. Just an office mouse, no RGB or high DPI/polling rate stuff.

 

Discrete mode (3070) - Idle 20W, playing youtube video 23W

Dynamic mode (optimus) - Idle 18W, playing youtube video 20W

 

So for my laptop I'm looking at around 11 to 15% increase from Optimus tech. However, I wonder if there is a software element to this that skews my results. I was also looking at the CPU, iGPU, dGPU powers in both cases. It looked like the dGPU was enabled in both cases, reporting >10W. The dGPU did not entirely shut off. If it did, that could result in more like a 2x battery life extension.

 

Currently the laptop is equivalent to around 4h from full battery life regardless of the setting. That's actually better than I'd expect for a gaming laptop.

[AMD A10-9600P]

8 minutes ago, porina said:

I just thought of a test which doesn't involve long running of the laptop. Basically the battery drain rate is reported so that is system power consumption. I used the same display brightness setting for both tests. A USB mouse is connected. Just an office mouse, no RGB or high DPI/polling rate stuff.

 

Discrete mode (3070) - Idle 20W, playing youtube video 23W

Dynamic mode (optimus) - Idle 18W, playing youtube video 20W

 

So for my laptop I'm looking at around 11 to 15% increase from Optimus tech. However, I wonder if there is a software element to this that skews my results. I was also looking at the CPU, iGPU, dGPU powers in both cases. It looked like the dGPU was enabled in both cases, reporting >10W. The dGPU did not entirely shut off. If it did, that could result in more like a 2x battery life extension.

 

Currently the laptop is equivalent to around 4h from full battery life regardless of the setting. That's actually better than I'd expect for a gaming laptop.

Ignoring the fact that that isn't a perfect test, that is still interesting stuff. That is better than I would have expected for a high powered GPU, but still does prove the need for an iGPU. Over a few hours that extra power draw from the dGPU will make a bigger and bigger difference to the battery life. I can't stress enough how important it is that my laptop has both an iGPU and dGPU. I use the iGPU 90% of the time, using Edge, Word, PowerPoint, iTunes, Mail and so on, and then use the dGPU if plugged in and wanting to do some 3D work. I do notice a lot more heat when using the dGPU, and also increased power draw on battery, as opposed to using the iGPU for the same tasks.

 

Unfortunately, I don't think dGPUs ever switch off entirely, it could be useful for manufacturers to have a kill switch for the dGPU to save battery on machines where users want the best of both worlds. That will have a larger impact with more powerful GPUs in particular, but I do know that my MX450 still has a fairly noticeable impact on battery life. I use an ASUS laptop that they also offer without the MX450 (in a slightly different shell), and as far as I know, battery life on the non-dGPU model is about 20% longer (up from around 10 hours to 12).

 

Entirely ignoring power draw, the iGPU can also have other advantages, for example, as the dGPU is not hooked up directly to the display, this means that it only has to run one program, like if you want to run an intensive game. For example, on my desktop I just have a 1660S dGPU, so that runs everything on the display, reducing available resources for the game I want to run, as opposed to on my laptop, where Nvidia's monitoring icon shows me that only 1 program uses the dGPU at a time, and everything else is ran off the iGPU, saving more resources on the more powerful dGPU for 3D tasks. This has less of an advantage when you step up to better GPUs like the 3070, but can make a big difference with lower powered GPUs like my MX450.