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gpu link speed

B

bigins

macrumors newbie
Original poster
Mar 30, 2020
8
2
hi just received new MacBook Pro 2019 system information reporting pice 8x AMD Radeon Pro 5500M just wondering if this is correct
Thanks Paul

Type: GPU


Bus: PCIe


PCIe Lane Width: x8


VRAM (Total): 8 GB


Vendor: AMD (0x1002)


Device ID: 0x7340


Revision ID: 0x0040


ROM Revision: 113-D3220E-190


VBIOS Version: 113-D32206U1-019


Option ROM Version: 113-D32206U1-019


EFI Driver Version: 01.01.190


Automatic Graphics Switching: Supported


gMux Version: 5.0.0


Metal: Supported, feature set macOS GPUFamily2 v1
 
Doesn't look correct. mine:

Chipset Model: AMD Radeon Pro 5500M
Type: GPU
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 8 GB
Vendor: AMD (0x1002)
Device ID: 0x7340
Revision ID: 0x0040
ROM Revision: 113-D3220E-190
VBIOS Version: 113-D32206U1-019
Option ROM Version: 113-D32206U1-019
EFI Driver Version: 01.01.190
Automatic Graphics Switching: Supported
gMux Version: 5.0.0
Metal: Supported, feature set macOS GPUFamily2 v1
 
Thanks for the replies - @thedocbwarren thank you for your reply that's exactly what I was expecting that it should be 16 and not 8, I am now also suffering kernel panics reporting problem with GPU after the MacBook has been asleep, I will be getting on to Apple - thanks Paul
 
I think 8x is normal, in order to free up pcie lanes for all the thunderbolt ports.

Mine certainly says 8x too.

yep, apple allocate 8x to gpu and 4x to each thunderbolt controller from cpu for performance, nvme and wifi run from platform controller.

For these gpu's, 8x is plenty.
 
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Not sure that's true as I don't see that with mine but who knows if it's a different config.

iMacDragon said:
I think 8x is normal, in order to free up pcie lanes for all the thunderbolt ports.

Mine certainly says 8x too.

yep, apple allocate 8x to gpu and 4x to each thunderbolt controller from cpu for performance, nvme and wifi run from platform controller.

For these gpu's, 8x is plenty.
Click to expand...
 
I have a 4K monitor plugged in via thunderbolt (not usb-c) to DisplayPort. I only have a usb-c hub with really only a usb external HDD for timemachine plugged in. Maybe this is the reason but I’ve never seen it display 8x under any circumstance.

iMacDragon said:
https://developer.apple.com/documentation/metal/gpu_selection_in_macos/understanding_gpu_bandwidth specifies that both 8x and 16x are possible depending on machine configuration, though I'm still wondering about your 16x as it does seem out of 'normal' for other 16"'s that I've seen values from.
Click to expand...
 
The PCI-e link on my maxed out CPU/GPU config is 8x. I am a bit surprised that some people get an 8x config and some 16x one, seems a bit random. Performance implications may or may not be there, depending on what you do. The 8x interface is dead slow compared with the GPU's internal bandwidth (around 25x slower)...
 
I have to believe something is allocating it differently for some reason. I maxed the cpu and gpu as well. Might need someone close to Apple to explain how this happens. I would assume it has to be a throttle for some reason (battery?)

leman said:
The PCI-e link on my maxed out CPU/GPU config is 8x. I am a bit surprised that some people get an 8x config and some 16x one, seems a bit random. Performance implications may or may not be there, depending on what you do. The 8x interface is dead slow compared with the GPU's internal bandwidth (around 25x slower)...
Click to expand...
 
bigins said:
8x and not 16x thanks paul
Click to expand...

Laptop (or consumer desktop) CPUs don't have many PCIe lanes, and thunderbolt ports take a lot of them. Apple laptops have thunderbolt ports.

The 5500M isn't exactly a blisteringly fast GPU, wasting 16 lanes on it would take away from other IO on the machine for little gain.
 
Yep I get that but some are at 16x and some at 8x So what’s going on and I had loads of gpu Kernel panics so I am waiting for my replacement to arrive I will let you know what this one reports back Also I was having heat issues when plugged in to an external monitor it was drawing nearly 20 W
[automerge]1586256325[/automerge]

[automerge]1586256593[/automerge]
Forgot to mention the link speed Did not change with external or internal monitor and Thinking about it What is the point Of having A fast external egup on a thunderbolt port if that’s only going to run at 4x Don’t make sense or I must be missing something
Thanks paul
 
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ok new MacBook and look what is going on 16x as it should be
IMG_0867.jpeg
 
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throAU said:
Laptop (or consumer desktop) CP
The 5500M isn't exactly a blisteringly fast GPU, wasting 16 lanes on it would take away from other IO on the machine for little gain.
Click to expand...

I don’t know what you mean by blisteringly fast here but it’s a GPU with almost 200 GB/s memory bandwidth. Compare it with 80 GB/s or something of Polaris. If you have an application that relies on streaming data between the CPU and the GPU, the x8 interface is woefully inadequate. Yes, it won’t matter for games (games are generally not streaming data), but productivity applications might see a hit.
 
YEs and 16x should be the correct bus speed for the dGPU. And the 5500m is actaully a good GPU considering we are talkoing about mobile. Would I like a 5700-level, yes, would I like Nvidia for ML/AI, yes, but we have a good dGPU to work with.

leman said:
I don’t know what you mean by blisteringly fast here but it’s a GPU with almost 200 GB/s memory bandwidth. Compare it with 80 GB/s or something of Polaris. If you have an application that relies on streaming data between the CPU and the GPU, the x8 interface is woefully inadequate. Yes, it won’t matter for games (games are generally not streaming data), but productivity applications might see a hit.
Click to expand...
 
Oh well, what can I say. The Mac updated to the latest software, and now my link speed has gone back down to 8x - I've enclosed an image. Don't know what's going on here, must be the update from 10.15.3 to 10.15.4 which must screw this up..
[automerge]1586464677[/automerge]
Could people please check that if you have a link speed of 16x and not 8x and you're on the latest version of 10.15.4 or whether you're still on 10.15.3 - thanks, Paul.
 

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Physically, the H-series Intel CPUs should only be using x8 for the dGPU, since they have a total of 16 PCIE lanes (not counting the ones hanging off the PCH).

From ark.intel.com

PCI Express Configurations: Up to 1x16, 2x8, 1x8+2x4
Max # of PCI Express Lanes: 16

I would expect the 16-inch MBP to have 1x8 going to the dGPU, 2x4 to the Thunderbolt 3 controllers (1x4 each). The T2 and other subsystems (Wifi) would hang off the PCH's integrated PCIE switch.
 
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Yep but it was showing 16x now 8 x and that is saying on your link that the maximum for the GPU is 16, so I don’t understand what you’re saying?
 
leman said:
I don’t know what you mean by blisteringly fast here but it’s a GPU with almost 200 GB/s memory bandwidth. Compare it with 80 GB/s or something of Polaris. If you have an application that relies on streaming data between the CPU and the GPU, the x8 interface is woefully inadequate. Yes, it won’t matter for games (games are generally not streaming data), but productivity applications might see a hit.
Click to expand...

By that, I mean that by the time you fill its VRAM and drop back to PCIe interface for streaming things over, performance will have tanked at that point anyway.

Apple made a trade of GPU lanes that would make virtually no difference to performance for Thunderbolt lanes.

littlepud said:
I would expect the 16-inch MBP to have 1x8 going to the dGPU, 2x4 to the Thunderbolt 3 controllers (1x4 each). The T2 and other subsystems (Wifi) would hang off the PCH's integrated PCIE switch.
Click to expand...

Exactly this. Intel consumer CPUs don't have many lanes. If Apple used the full 16 for the GPU they would not have enough for the thunderbolt ports. They made a measured trade-off that won't have any appreciable impact to GPU performance.
 
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Ok so you tell me why it was at 16 now 8 and getting kernel panics again I don’t make sense
 
mac OS Catalina 10.16.6 has just released. I'm not sure if this can change back to x16, and very concerned to update for now.
 
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