XPS 15 - 9550 not able to reach 40Gbps over TB3?
 
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[Solved] XPS 15 - 9550 not able to reach 40Gbps over TB3?  

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jscinoz
(@jscinoz)
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Such a shame to hear about this issue, I bought a XPS 15 9550 early last year and have been pretty happy with it, but was looking into some kind of eGPU setup for better performance and to alleviate some thermal issues, but I've concerns as to whether it'd be much of a worthwhile improvement given the bandwidth limitations.

Looking forward to see if Dell has anything to say about this, since they quite clearly advertised these machines as supporting TB3, and TB3 at a heavily reduced link-speed is really not the same thing.

Has anyone with the requisite electrical knowledge been able to discern if things are at least physically wired up correctly for x4 speeds? That would at least give us hope for a BIOS fix.

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

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nando4
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XPS 9350 has a x2 3.0 electrically wired TB3 controller

@jscinoz, unfortunately bad news. I managed to find a XPS 9350 schematic and it's Thunderbolt controller is electrically wired as x2 3.0. The snippet below is from pg 11 of DELL_XPS_13-9350_AAZ80_LA-C881P_r1.0_A00.pdf  where we see this. Alpine Ridge is the TB3 controller

No amount of BIOS fixes can the get x4 3.0 32Gbps performance on these systems.

I can't find a XPS 9550/9360 schematic but this is a bad sign that they too are more likely than not to be x2 3.0 (16Gbps) electrically wired too given they have a port13+15 x2 3.0 arrangement, with TB3 hanging off port15. Only port13 can be BIOS set as x4 3.0.

 
XPS 9350 TB x2

 

What to do about this 16Gbps TB3 controller?

Time to ask for refunds, replacement systemboards using x4 3.0 electrical connections or replacement systems like Dell Precision M3510/M7510 from Dell. Those systems are *believed* to run x4 3.0 32Gbps, but require further investigation to be 100% sure.

eGPU Setup 1.35    •    eGPU Port Bandwidth Reference Table

 
2015 15" Dell Precision 7510 (Q M1000M) [6th,4C,H] + GTX 1080 Ti @32Gbps-M.2 (ADT-Link R43SG) + Win10 1803 // compares M.2 vs TB3 performance inc unoptimized H-CPU BIOS [build link]  


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jscinoz
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@nando: Ah, thank you for the information, that is quite the shame. I suppose it's not the end of the world, as the performance drop (when using an external) display isn't too significant, but this certainly hinders things for internal display usage.

All said though, this really does seem like a bit of false advertising on Dell's part; they're advertising these machines as having TB3 support and specifically stating it offers 40Gbps throughput (here, ctrl-f 40Gbps), yet in reality these machines' Thunderbolt implementation is rather crippled (I am curious as to whether the specification itself allows for reduced link speeds, but that's another matter and not particularly relevant).

I'll get in touch with Dell when I have some time and see if they've anything more to add on the matter. Thankfully we've got very strong consumer protection laws down here, so if Dell's not willing to rectify this for the many customers who were misled, there's still further avenues to pursue.

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

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Captainali
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let us know what they say after you complain. I'm keen to hear what they will do. Thanks

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

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nando4
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A reddit user pointed out that TB3 traffic is PCIe+DP so additional DP pathway traffic could still mean the TB3 link delivers 40Gbps of traffic, even with a 16Gbps neutered PCIe link.

However, that argument falls apart by referring to Intel's own TB3  “4 lanes of PCI Expresss 3.0” spec  here. Dell XPS 9350/9350/9550 and Precision M5510 are not compliant. They are all running a 16Gbps x2 3.0 TB3 PCIe link - "2 lanes of PCI Express 3.0" in Intel speak.

Posted by: jscinoz

 

@nando: Ah, thank you for the information, that is quite the shame. I suppose it's not the end of the world, as the performance drop (when using an external) display isn't too significant, but this certainly hinders things for internal display usage.

All said though, this really does seem like a bit of false advertising on Dell's part; they're advertising these machines as having TB3 support and specifically stating it offers 40Gbps throughput (here, ctrl-f 40Gbps), yet in reality these machines' Thunderbolt implementation is rather crippled (I am curious as to whether the specification itself allows for reduced link speeds, but that's another matter and not particularly relevant).

I'll get in touch with Dell when I have some time and see if they've anything more to add on the matter. Thankfully we've got very strong consumer protection laws down here, so if Dell's not willing to rectify this for the many customers who were misled, there's still further avenues to pursue.

   

eGPU Setup 1.35    •    eGPU Port Bandwidth Reference Table

 
2015 15" Dell Precision 7510 (Q M1000M) [6th,4C,H] + GTX 1080 Ti @32Gbps-M.2 (ADT-Link R43SG) + Win10 1803 // compares M.2 vs TB3 performance inc unoptimized H-CPU BIOS [build link]  


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nando4
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Dell XPS 9560 specs are out. A replacement for the TB3 neutered XPS 9550?

In the eGPU laptop candidate list (Only Thunderbolt 3 and faster) Doug Bates wrote:

Finally, a lightweight quad core with TB3. Combine this with ASUS XG Station 2, for instance, and a good desktop GPU and we finally have true portability with full on gaming when docked.

4lb Dell XPS 15 9560 with quad-core i7 7700HQ GTX1050 specs list TB3 with 1 cable charging

https://archive.fo/GF2eN

http://www.notebookcheck.net/XPS-15-9560-official-GTX-1050-Kaby-Lake-fingerprint-scanner-and-Windows-Hello.188069.0.html

eGPU Setup 1.35    •    eGPU Port Bandwidth Reference Table

 
2015 15" Dell Precision 7510 (Q M1000M) [6th,4C,H] + GTX 1080 Ti @32Gbps-M.2 (ADT-Link R43SG) + Win10 1803 // compares M.2 vs TB3 performance inc unoptimized H-CPU BIOS [build link]  


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XCVG
 XCVG
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A reddit user pointed out that TB3 traffic is PCIe+DP so additional DP pathway traffic could still mean the TB3 link delivers 40Gbps of traffic, even with a 16Gbps neutered PCIe link.

However, that argument falls apart by referring to Intel's own TB3  “4 lanes of PCI Expresss 3.0” spec  here. Dell XPS 9350/9350/9550 and Precision M5510 are not compliant. They are all running a 16Gbps x2 3.0 TB3 PCIe link - "2 lanes of PCI Express 3.0" in Intel speak.

The exact marketing copy they used (at least in my country) is "40gbps of data, 8x faster than USB 3.0". While one could interpret the DP bandwidth to be "data", it is pretty misleading.

Time to ask for refunds, replacement systemboards using x4 3.0 electrical connections or replacement systems like Dell Precision M3510/M7510 from Dell. Those systems are *believed* to run x4 3.0 32Gbps, but require further investigation to be 100% sure.

What about the Alienware 13 and 15? In any case, a dissimilar replacement isn't really a good answer. I bought this laptop for certain (advertised) features including but not limited to eGPU.

Finally, a lightweight quad core with TB3. Combine this with ASUS XG Station 2, for instance, and a good desktop GPU and we finally have true portability with full on gaming when docked.

4lb Dell XPS 15 9560 with quad-core i7 7700HQ GTX1050 specs list TB3 with 1 cable charging

https://archive.fo/GF2eN

http://www.notebookcheck.net/XPS-15-9560-official-GTX-1050-Kaby-Lake-fingerprint-scanner-and-Windows-Hello.188069.0.html

Fingers crossed, but given that the 9360 seems to be crippled like the 9350 there's a good chance the 9560 is the same as the 9550.

 

2015 15" Dell XPS 15 9550 (GTX960M) [6th,4C,H] + GTX 1080 @ 16Gbps-TB3 (Mantiz Venus) + Win10 [build link]  

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Senorspam
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Seems like Notebookcheck did an article about it - http://www.notebookcheck.net/Design-flaw-in-XPS-9350-9550-may-cause-TB3-ports-to-run-at-TB2-speeds.189743.0.html . Hopefully that brings more light to this issue. If Dell doesn't offer a official response or propose a satisfactory solution in the support emails, it seems like all we can do is report it to the FTC (for US users) - https://www.ftccomplaintassistant.gov/GettingStarted?NextQID=70&Url=%23%26panel1-6#crnt . Doubt it will do too much, but if enough people submit them, it just may cause the FTC to help us out with this issue. It wouldn't be as upsetting if Dell didn't use the term "40Gbps" 10 times on the XPS 15 9550 page, its quite misleading.

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

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nando4
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Douglas has pieced together a notebookcheck.net article from an email draft I sent. I requested he wait a bit for a more in-depth post I was creating here.

Anyway, 40Gbps can be still be achieved across the TB3 channel by say 16Gbps PCIe + 24Gbps DP of traffic.  Thunderbolt3 carries both traffic types. So the 40Gbps is not the issue.

The issue is:

The Dell XPS 9350/9360/9550 and Precision M5510 are all running a 16Gbps x2 3.0 PCIe link to the TB3 controller rather than the 32Gbps x4 3.0 specced by Intel “4 lanes of PCI Expresss 3.0”  here.   PCIe TB3 peripherals such as storage and eGPUs will then have approx 50% less peak bandwidth.

 

The picture below summarizes the problem:

 

Continue reading next post to see how Intel is the instigator of this misleading specification . . .

eGPU Setup 1.35    •    eGPU Port Bandwidth Reference Table

 
2015 15" Dell Precision 7510 (Q M1000M) [6th,4C,H] + GTX 1080 Ti @32Gbps-M.2 (ADT-Link R43SG) + Win10 1803 // compares M.2 vs TB3 performance inc unoptimized H-CPU BIOS [build link]  


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nando4
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Intel Thunderbolt3 documentation specifying TB3 as being 2-4 lanes of PCIe 3.0 clears Dell of any wrongdoing

Intel TB3 specs here (pg5) tell us single-TB3 port systems can run between 2-4 lanes of PCIe 3.0. In which case, Dell are clear of any wrongdoing.

Relevant pg5 snippet from https://thunderbolttechnology.net/sites/default/files/HBD16235_Thunderbolt_TB_r05.pdf quoted and highlighed below:

A Thunderbolt 3 port requires that each connector be provided with at least:
 
• The equivalent of two lanes of PCI Express Gen 3 data
• One full DisplayPort 1.2a (four-lane) interface
 
Starting with Intel systems based on the 100 Series chipset, Thunderbolt 3 is delivered via a series of discrete silicon devices that have varying capabilities. The dual-port SKU supports two Thunderbolt 3 connectors. It takes four lanes of PCI Express Gen 3 as an input and two full (four-lane) links of DisplayPort 1.2a.
 
The single-port SKU supports a single Thunderbolt 3 connector.
 
In general, if a system has a single Thunderbolt 3 port, the connectivity behind that port could be as high as four lanes of PCI Express Gen 3 with dual DisplayPort links. It could also be as little as two lanes of PCI Express Gen 3, with a single DisplayPort link.
 
In each case, the Thunderbolt interface itself doesn’t change; it is still 40 Gbps. However, the underlying source data and display may be more limited.
 

It means us eGPU users must be very careful when selecting candidate eGPU systems. Those with a single port require scrutiny to confirm is running 4 rather than 2 lanes of PCIe 3.0 if we wish to have 32Gbps of PCIe bandwidth rather than the TB2-spec of 16Gbps.

 
Misleading Intel advertising
 
The devil is in the detail. Why is Intel advertising TB3 as "4 lanes of PCIEe 3.0" rather than "up to 4 lanes of PCIe 3.0" then hide in the detailed docs that it might be 2?  This is misleading advertising on Intel's part. I can understand if affected Dell system owners feel cheated by this.
 
What can Dell do to help eGPU users?
 
By upgrading to a full 32Gbps x4 3.0 TB3 port on revised products such as the XPS 9560. Two TB3 ports even.

Otherwise late 2016 13" and 15" Macbooks and 13" HP Spectre 360 systems  are superior for eGPU use as they do provide full 32Gbps x4 3.0 TB3 PCIe ports.
 
 
 
 

eGPU Setup 1.35    •    eGPU Port Bandwidth Reference Table

 
2015 15" Dell Precision 7510 (Q M1000M) [6th,4C,H] + GTX 1080 Ti @32Gbps-M.2 (ADT-Link R43SG) + Win10 1803 // compares M.2 vs TB3 performance inc unoptimized H-CPU BIOS [build link]  


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