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Blame Intel if you feel eGPU sucks, cuz U series CPU it self is the biggest bottleneck!

TL DR: All bandwidth that U series CPU got is 4GB/s max duplex, can even be as low as 2GB/s fixed (DIMM channels not included)

 

As is mentioned in a former video in LTT, eGPU tends to suffer in terms of performs due to bottlenecking.
Most complaints claims that the 40Gbps Thunderbolt3 link is the major issue.
I used to make such complaints too, but it all changed TODAY

Just bear with me, I'll explain it

I was chatting with one of my friends and then we begin to discuss on whether eGPU over Thunderbolt3 is a good idea

And he was like "the total bandwidth running through the U series CPUs(DRAM channels NOT included) is only 4GB/s or 2GB/s"

I didn't take it either in the first place, and then we dug a bit on Intel's datasheet

Link https://www.intel.com/content/www/us/en/processors/core/7th-gen-core-family-mobile-u-y-processor-lines-i-o-datasheet-vol-1.html
1075339158_2018-10-1520_46_30.png.434866c9ff4c0236a634b6222d905068.png
Page 20 says total bandwidth to PCH-U is 4GT/s (OPI= Onboard DMI Interconnect Port Interface) roughly 4GB/s duplex

1647563510_2018-10-1520_49_24.thumb.png.3e68a32170eeab0dc3e6190a9bd5e5cf.png

469696042_2018-10-1520_48_26.png.0fe66dec2214311532bd9a9e32c4b182.png

Page 25 says 16 HSIO lanes translates to 12 PCIe lanes, exactly what we're using!
WTF??
This indicates that all in/out-coming bandwidth we got is merely 4GB/s tops!
And it can also be configured to 2GB/s for power saving(can be configured at a fixed state)
Techpowerup indicates that Gen3 x4 link doesn't create noticeable ( <5%) bottlenecking 

https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1080_PCI_Express_Scaling/24.html

I supposed this is exactly why bottlenecking is so disastrous on U series GPU
I can't understand why will Intel do this 
Why did they remove PCIe controllers from CPU?
 

Edited by Defconed
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You're trying to use an ultra-low power mobile integrated-everything CPU to drive a fat external GPU? Lack of CPU power is probably worse than the connectivity bandwidth.

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You are aware that 30Gbps translates to roughly 4GB/s?

I guess the answer is not that simply you might think

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2 minutes ago, porina said:

You're trying to use an ultra-low power mobile integrated-everything CPU to drive a fat external GPU? Lack of CPU power is probably worse than the connectivity bandwidth.

Agreed, PCIe x4 doesn't limit a gpu that much in gaming compared to 16x, it's the CPU that can't keep up with everything that needs to be drawn.

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yes....... 4GB/s is exactly what we would expect (or roughly its actually slighly lower).

 

4x PCIe only gives 4GB/s.

 

which bottlenecks quite a few cards, what is new here?

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2 minutes ago, porina said:

You're trying to use an ultra-low power mobile integrated-everything CPU to drive a fat external GPU? Lack of CPU power is probably worse than the connectivity bandwidth.

what I don't understand is that they totally removed PCIe controllers from CPU die
I don't see moving controllers to PCH gives any reasonable power optimization
 

 

3 minutes ago, 19_blackie_73 said:

You are aware that 30Gbps translates to roughly 4GB/s?

I guess the answer is not that simply you might think

what I am able to google indicates that this"OPI" is basically DMI3.0 or something alike
It's not gonna be better than than 4GB/s
BTW , what I saw was 8GT/s, didn't see any"30Gbps"
Try prove me wrong, I'm also short on data

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13 minutes ago, GoldenLag said:

yes....... 4GB/s is exactly what we would expect (or roughly its actually slighly lower).

 

4x PCIe only gives 4GB/s.

 

which bottlenecks quite a few cards, what is new here?

Thing is, the whole chip only has 4GB/s
either your SSD or USB or anything else can steal from it
And I can't understand why they removed PCIe controllers from CPU die, where's the point of it?
Also, certain manufacturers set it at 2GB/s
I guess that's even worse

Edited by Defconed
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Just now, Defconed said:


And I can't understand why they removed PCIe controllers from CPU die, where's the point of it?

Saves power, this allows you to turn of the PCIe controller completely, instead of low power mode.(In sleep) It also allows for choises in what controller you want.

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2 minutes ago, timl132 said:

Saves power, this allows you to turn of the PCIe controller completely, instead of low power mode.(In sleep) It also allows for choises in what controller you want.

I've heard rumors saying that only TB3 eGPU over PCH can be hotplugged( or say, hot-unplugged), does that makes sense?
4GB/s total for a whole system still seems too embarrassing for a system with GPU

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1 minute ago, Defconed said:

Thing is, the whole chip only has 4GB/s
either your SSD or USB or anything else can steal from it
And I can't understand why they removed PCIe controllers from CPU die, where's the point of it?

And i didnt notice the multiplexing. Srry

 

Isnt all that surprising tbh. There is probably some resoning behind it

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Just now, Defconed said:

I've heard rumors saying that only TB3 eGPU over PCH can be hotplugged( or say, hot-unplugged)

That's more or less the point of an external connector, to be hot-plugged. I believe I saw Linus do it a few times in a vid, so yes, it's possible.

1 minute ago, Defconed said:

4GB/s total for a whole system still seems too embarrassing for a system with GPU

It's not made to have a high end GPU connected to it, it's designed to be minimal and be just enough for whatever a low power laptop is needed for. A SSD and a HDD would combined need about 800MB/S, and there are some USB devices, so let's say you are left with 3GB/s, that seems quite reasonable for a low power laptop/cpu to me. Considering they are made to have like an 1050 connected to them or something, plus, everything would be CPU bottlenecked anyway.

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3 minutes ago, GoldenLag said:

And i didnt notice the multiplexing. Srry

 

Isnt all that surprising tbh. There is probably some resoning behind it

Originally I thought it was 12lanes direct attached to CPU and highly "splitable"
I was like "Yeah, Intel can split PCIe lanes, if they want"
And today I was like
"wtf it's all PCHed PCIe lanes??"
Wonder how much bandwidth will be stealed by storage, network & etc

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4 minutes ago, timl132 said:

That's more or less the point of an external connector, to be hot-plugged. I believe I saw Linus do it a few times in a vid, so yes, it's possible.

It's not made to have a high end GPU connected to it, it's designed to be minimal and be just enough for whatever a low power laptop is needed for. A SSD and a HDD would combined need about 800MB/S, and there are some USB devices, so let's say you are left with 3GB/s, that seems quite reasonable for a low power laptop/cpu to me. Considering they are made to have like an 1050 connected to them or something, plus, everything would be CPU bottlenecked anyway.

One of TB3's biggest selling point is eGPU, while Intel is making it all less useable with debuffed PCIe
Also, certain thin&lights do have stuff like 1050/1060MaxQ
Guess that the manufacturers knew this is gonna happen, but they just don't talk about it
Btw, at 15W, stuff like 8250U can perform nearly as a 6300HQ
It can even be something like 7700HQ if you free TDP to 25W with XTU

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1 hour ago, porina said:

You're trying to use an ultra-low power mobile integrated-everything CPU to drive a fat external GPU? Lack of CPU power is probably worse than the connectivity bandwidth.

 

1 hour ago, timl132 said:

Agreed, PCIe x4 doesn't limit a gpu that much in gaming compared to 16x, it's the CPU that can't keep up with everything that needs to be drawn.

My memory served me right
https://www.cpubenchmark.net/high_end_cpus.html
Stock 8250u behaves better than 7300HQ, slight worse than i5 6600
I guess we can call 7300HQ a fairly mainstream gaming laptop config for 1 year ago,  don't think we can call that too much of a bottlenecking
If you do, you'll need to admit that a gaming laptop is more bottlenecking than the thin&light we're talking about

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7300HQ is typically paired with lower GPUs and not high fps displays. It's ok for that is it will be more GPU limited. 8250u us intended to drive iGPU, it is ok for that. If you pair either with a 1070 or higher, it may start to limit the GPU putting aside bandwidth concerns. Any gaming laptop with faster GPUs would more likely have 7700HQ.

TV Gaming system: Asus B560M-A, i7-11700k, Scythe Fuma 2, Corsair Vengeance Pro RGB 3200@2133 4x16GB, MSI 3070 Gaming Trio X, EVGA Supernova G2L 850W, Anidees Ai Crystal, Samsung 980 Pro 2TB, LG OLED55B9PLA 4k120 G-Sync Compatible
Streaming system: Asus X299 TUF mark 2, i9-7920X, Noctua D15, Corsair Vengeance LPX RGB 3000 8x8GB, Gigabyte 2070, Corsair HX1000i, GameMax Abyss, Samsung 970 Evo 500GB, Crucial BX500 1TB, BenQ XL2411 1080p144 + HP LP2475w 1200p60
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5 minutes ago, porina said:

7300HQ is typically paired with lower GPUs and not high fps displays. It's ok for that is it will be more GPU limited. 8250u us intended to drive iGPU, it is ok for that. If you pair either with a 1070 or higher, it may start to limit the GPU putting aside bandwidth concerns. Any gaming laptop with faster GPUs would more likely have 7700HQ.

The problem is that the i5-8250U is pretty much the same in terms of performance as the i7-7700HQ :P I wonder if the 7700HQ has more lanes at its disposal for running eGPUs.
I know the R5 2500U in my laptop could have this problem as well due to PCIE lanes limit put by the iGPU on the chip. The RX 560 is enough for now though.

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1 minute ago, Morgan MLGman said:

The problem is that the i5-8250U is pretty much the same in terms of performance as the i7-7700HQ :P I wonder if the 7700HQ has more lanes at its disposal for running eGPUs.
I know the R5 2500U in my laptop could have this problem as well due to PCIE lanes limit put by the iGPU on the chip. The RX 560 is enough for now though.

yup thats correct, 7700HQ has 16 pcie lanes while 8250U has 12. This is interesting.

mY s YsTeM iS Not pErfoRmInG aS gOOd As I sAW oN yOuTuBe. WhA t IS a GoOd FaN CuRVe??!!? wHat aRe tEh GoOd OvERclok SeTTinGS FoR My CaRd??
 HoW CaN I foRcE my GpU to uSe 1o0%? BuT WiLL i HaVE Bo0tllEnEcKs? RyZEN dOeS NoT peRfORm BetTer wItH HiGhER sPEED RaM!!dId i WiN teH SiLiCON LotTerrYyOu ShoUlD dEsHrOuD uR GPUmy SYstEm iS UNDerPerforMiNg iN WarzONEcan mY Pc Run WiNdOwS 11 ?woUld BaKInG MY GRaPHics card fIX it?
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3 minutes ago, porina said:

7300HQ is typically paired with lower GPUs and not high fps displays. It's ok for that is it will be more GPU limited. 8250u us intended to drive iGPU, it is ok for that. If you pair either with a 1070 or higher, it may start to limit the GPU putting aside bandwidth concerns. Any gaming laptop with faster GPUs would more likely have 7700HQ.

7700HQ  8844
8250u 7665
Yeah.. there surely is a distance between them, but given that its "thin and light with eGPU" setup, I suppose it's good enough. It's more of a product arrangement thing. e.g: the i9 on MacbookPro(before thermal bug fix, it's a joke)
There surely is a reason that Gigabyte throw a 1070 into their dock, I'd say that a 1060 or a 1070 can fulfill most requirements, and a 8250u can do fairly well powering these buddies
That's why I'm complaining about 4GB/s
Also, in case you missed it, storage , ethernet and USB also slice their part from the 4GB/s
And there are laptops with 2GB/s bandwidth, I think that's going way too far

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Just now, Levent said:

yup thats correct, 7700HQ has 16 pcie lanes while 8250U has 12. This is interesting.

12lanes( in fact 16 HSIO lanes) through a 4GB/s bottleneck (shared with USB Ethernet storage and stuff)
I wonder what's in Intel's mind when they designed this

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Just now, Defconed said:

12lanes( in fact 16 HSIO lanes) through a 4GB/s bottleneck (shared with USB Ethernet storage and stuff)
I wonder what's in Intel's mind when they designed this

yeah that also makes me wonder.

mY s YsTeM iS Not pErfoRmInG aS gOOd As I sAW oN yOuTuBe. WhA t IS a GoOd FaN CuRVe??!!? wHat aRe tEh GoOd OvERclok SeTTinGS FoR My CaRd??
 HoW CaN I foRcE my GpU to uSe 1o0%? BuT WiLL i HaVE Bo0tllEnEcKs? RyZEN dOeS NoT peRfORm BetTer wItH HiGhER sPEED RaM!!dId i WiN teH SiLiCON LotTerrYyOu ShoUlD dEsHrOuD uR GPUmy SYstEm iS UNDerPerforMiNg iN WarzONEcan mY Pc Run WiNdOwS 11 ?woUld BaKInG MY GRaPHics card fIX it?
 MultimETeR TeSTiNG!! aMd'S GpU DrIvErS aRe as goOD aS NviDia's YOU SHoUlD oVERCloCk yOUR ramS To 5000C18

 

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5 minutes ago, Morgan MLGman said:

The problem is that the i5-8250U is pretty much the same in terms of performance as the i7-7700HQ :P I wonder if the 7700HQ has more lanes at its disposal for running eGPUs.
I know the R5 2500U in my laptop could have this problem as well due to PCIE lanes limit put by the iGPU on the chip. The RX 560 is enough for now though.

nope splitting is different
desktop/ S series can only do 8+4+4 lanes distribution on direct lanes
also, as someone mentioned above, does throwing all PCIe lanes over PCH helps saving power?
PS: my wild guess is that 2700U should not be affected by this problem, I think I need a AMD Ark to confirm this

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2 minutes ago, Levent said:

yeah that also makes me wonder.

the real disaster is that certain laptops actually put it to a static 2GB/s
This also makes me wonder how much bandwidth ( for storage) do we actually needs

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2 hours ago, Defconed said:

what I am able to google indicates that this"OPI" is basically DMI3.0 or something alike
It's not gonna be better than than 4GB/s
BTW , what I saw was 8GT/s, didn't see any"30Gbps"
Try prove me wrong, I'm also short on data

I referred to the named bandwith of tb3

GUITAR BUILD LOG FROM SCRATCH OUT OF APPLEWOOD

 

- Ryzen Build -

R5 3600 | MSI X470 Gaming Plus MAX | 16GB CL16 3200MHz Corsair LPX | Dark Rock 4

MSI 2060 Super Gaming X

1TB Intel 660p | 250GB Kingston A2000 | 1TB Seagate Barracuda | 2TB WD Blue

be quiet! Silent Base 601 | be quiet! Straight Power 550W CM

2x Dell UP2516D

 

- First System (Retired) -

Intel Xeon 1231v3 | 16GB Crucial Ballistix Sport Dual Channel | Gigabyte H97 D3H | Gigabyte GTX 970 Gaming G1 | 525 GB Crucial MX 300 | 1 TB + 2 TB Seagate HDD
be quiet! 500W Straight Power E10 CM | be quiet! Silent Base 800 with stock fans | be quiet! Dark Rock Advanced C1 | 2x Dell UP2516D

Reviews: be quiet! Silent Base 800 | MSI GTX 950 OC

 

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30 minutes ago, 19_blackie_73 said:

I referred to the named bandwith of tb3

Intel claimed 40Gbps, and so does everything I see..
I'm not familiar with the 120b/128b sort of coding stuff.. so I usually just call it by its actual bandwidth( in GiB/GB)

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1 hour ago, Morgan MLGman said:

The problem is that the i5-8250U is pretty much the same in terms of performance as the i7-7700HQ :P I wonder if the 7700HQ has more lanes at its disposal for running eGPUs.

Bleh, finding the various core turbo speeds of mobile processors isn't proving to be easy, and that's without taking into consideration the mobile parts are more likely to go into thermal limiting. My gut feeling is still that CPU would be limiting if you part it with a higher end GPU. If you use a lower end GPU, it would be GPU limiting. The bandwidth is probably not as significant in either case.

7 minutes ago, Defconed said:

Intel claimed 40Gbps, and so does everything I see..

Quick question, where exactly is the thunderbolt controller connected? To the chipset?

TV Gaming system: Asus B560M-A, i7-11700k, Scythe Fuma 2, Corsair Vengeance Pro RGB 3200@2133 4x16GB, MSI 3070 Gaming Trio X, EVGA Supernova G2L 850W, Anidees Ai Crystal, Samsung 980 Pro 2TB, LG OLED55B9PLA 4k120 G-Sync Compatible
Streaming system: Asus X299 TUF mark 2, i9-7920X, Noctua D15, Corsair Vengeance LPX RGB 3000 8x8GB, Gigabyte 2070, Corsair HX1000i, GameMax Abyss, Samsung 970 Evo 500GB, Crucial BX500 1TB, BenQ XL2411 1080p144 + HP LP2475w 1200p60
Gaming laptop: Lenovo Legion, 5800H, DDR4 3200C22 2x8GB, RTX 3070, SK Hynix 512 GB + Crucial P1 TB SSD, 165 Hz IPS 1080p G-Sync Compatible

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