The Makings of a Good Thunderbolt 3 Host - Dell Precision 7520 Review
eGPU.io launched on Thanksgiving weekend of 2016. It has been a blessing to have grown so quickly to become the place for external graphics card resources and discussion. We're very grateful for the help and participation of everyone involved. Our reviews thus far have focused primarily on Thunderbolt 3 enclosures, aka eGPU devices. The other major component of an eGPU pairing is the Thunderbolt 3 host. We've tried many ultrabooks, gaming laptops, and even built an ATX test bench in our quest to learn more about Thunderbolt 3 eGPU performance.
This review of a Dell Precision 7520 serves as an unofficial guide to help eGPU enthusiasts choose an appropriate Thunderbolt 3 host. With that in mind, let's identify the three primary types of computers suitable for eGPU.
|Ultrabook||+ Thin and Light||- Low-power processor|
|Mobile Workstation||+ Effective Cooling||- Bulky and heavy|
|SFF Desktop||+ Smaller Footprint||- Expensive compared to Desktop|
The dozen or so computers we've tested revealed many previously undocumented performance hindrances in running an eGPU. The first such finding was x2 PCIe lanes in Dell XPS laptops, reported by Splitframe. Nando4 summarized the performance advantage of a Thunderbolt 3 PCIe connection direct attachment to the CPU vs. one over the PCH. Most recently, I was dumbfounded when an Alienware 13 R2 + Graphics Amplifier eGPU setup was running at half-bandwidth. The culprit was the vendor's use of low-power GT2 mode (~ x2 PCIe 3.0) rather than high-performance GT4 mode (x4 PCIe3.0) in Skylake and Kaby Lake "U" processors.
Through trial and error, we've determined the best Thunderbolt 3 host for external graphics is a computer with a quad-core CPU, integrated GPU only, and direct x4 PCIe 3.0 connection to the CPU. This unicorn does not yet exist as far as we know. There are a handful of computers which have quad-core CPU with iGPU only. However, the PCIe 3.0 over Thunderbolt 3 connection is often times routed through the PCH and in worst case scenario runs at half-bandwidth. Please let us know if you're aware of such a creature in the wild. For the time being, we've made due with what's currently available.
The Dell Precision 7520 has many of the elements of the mythical creature we're looking for. Being a mobile workstation, it's built with a beefy cooling system and enclosed in a bulky form factor. The design could be mistaken for a laptop sold 10 years ago. There's no camera on the top of the display. There's no fancy lighting effects. What it does have are the bits that eGPU enthusiasts want. The processor is a quad-core Intel 7th generation Kaby Lake i5-7300HQ. The only graphics card is an Intel HD 630 iGPU. Last but not least, its PCIe 3.0 connection over Thunderbolt 3 is running with full 4 lanes through the PCH.
Many would question the desire for iGPU only in a performance laptop. There are two primary factors for this recommendation. Besides ease of eGPU setup, iGPU-only hosts have much longer battery life compared to their iGPU & dGPU counterparts. I've observed the 72 Wh battery lasting more than 8 hours on a single charge when I was using this Precision 7520 for web browsing and office tasks. Another bonus is the lack of heat and noise. The fans were inaudible during normal usage. In fact, the only time I've heard the fan noise and felt some exhaust heat were during gaming benchmarks. The noise and heat levels from the eGPU were much higher than those emitted by the Dell Precision 7520's cooling system.
This is a drastic difference from gaming laptops that I tested. They ran hot, noisy, and exhibited short battery life even when I didn't need the performance of the discrete GPU. Other than the Thunderbolt 3 MacBook Pros, most ultrabooks I tested have rather annoying cooling behaviors. Due to their thin profile, heat sinks and fins alone cannot dissipate heat quickly enough. Frequent intervals of fans running at full blast occur regularly whether the ultrabook is idle or not.
Testings & Benchmarks
I ran this Dell Precision 7520 through Specviewperf 12.1 and compared the results with our Z170 Thunderbolt 3 Test Bench. The eGPU device is a Sonnet Breakaway Box 350 paired with a Gigabyte Radeon RX 580.
The performance difference is marginal between this Dell Precision 7520 and the Z170 Test Bench. Even though this machine is not intended for PC gamers, it's one of the best Thunderbolt 3 hosts I've found for gaming with an eGPU. I ran it through a few gaming benchmarks in both internal and external display modes to provide a general idea.
|Radeon RX 580 eGPU||Precision 7520 Internal Display||Precision 7520 External Display||Z170 Test Bench|
|Unigine Valley||47.0 FPS||49.2 FPS||50.8 FPS|
|Unigine Heaven||47.1 FPS||48.7 FPS||49.2 FPS|
|Unigine Superposition||54.2 FPS||57.6 FPS||55.3 FPS|
|3DMark Time Spy||26.7 FPS||27.6 FPS||27.4 FPS|
|3DMark Fire Strike||56.4 FPS||57.1 FPS||57.0 FPS|
|Rise of the Tomb Raider||55.7 FPS||57.2 FPS||58.0 FPS|
|Tom Clancy's Ghost Recon||39.3 FPS||43.1 FPS||41.5 FPS|
|Shadow of Mordor||69.7 FPS||87.0 FPS||83.3 FPS|
Again, we see virtually no difference in eGPU performance between the Z170 Test Bench and the Dell Precision 7520. The latest AMD Xconnect software yields great results for eGPU internal display mode. As long as the Thunderbolt 3 host runs with 4 PCIe lanes, you can expect single-digit percentage performance loss when eGPU accelerates the internal display.
The Dell Precision 7520 is a blueprint for the makings of a good Thunderbolt 3 host. The only missing feature is a direct Thunderbolt 3 connection to the CPU. While it's not as stylish or portable as many slender ultrabooks, its effective cooling system prevents thermal throttling and emits low noise level during heavy use. To me, the trade-off is well worth it.
Thanks for the nice write-up, @itsage! I am currently on the hunt for a new notebook that can serve as an upgradeable/portable Thunderbolt 3 (TB3) eGPU host "unicorn," as well, and found your Dell Precision 7520 review to be a great starting point. I am most interested in the "mobile workstation" host type you describe for intensive 3D modelling and light VR visualization of these 3D renderings.
What are your thoughts/experience with using the HP ZBook Studio G4 as eGPU host for the above case? The ZBook G4 can be configured with 7th-gen quad-core i7 HQ or Xeon processors, and the i7's can even be configured with an integrated GPU only (optional NVIDIA Quadro M1200 GPU). From what I have found, it looks like the ZBooks have 4x PCIe 3.0 lanes for TB3 connections as opposed to the 2x variants in other laptops, but I am still not sure if the ZBook has a PCIe 3.0 connection directly to the CPU or if it is routed through the PCH. Finally, the starting ZBook G4 weight (4.4 lbs) is a bit lighter than the Dell Precision 7520 (6.2 lbs) and Lenovo ThinkPad P51 (5.6 lbs, another possible candidate), although this might balance out when you upgrade the ZBook to its (more realistic IMO) 93 WHr battery.
Another possibility would be the i7 HQ variant of the Dell Latitude 5480, which has to be configured with a NVIDIA GeForce 930MX GPU for TB3 capabilities. Again, unsure about the number of PCIe lanes and connectivity, but could be a good fit for a TB3 eGPU host. As an aside, it is a shame that the Lenovo ThinkPad T470p does not have TB3 connectivity - it could have been a really nice eGPU host setup!
I would love to know your thoughts. Also, how do you think the new Intel 8th gen processors (supposedly 4-core and 6-core CPUs - we'll know soon enough) might play into your search for the TB3 eGPU host "unicorn."
So I happen to own the previous generation Dell Precision 7510 that also has a dGPU Quadro M2000M 4GB card. I am interested in connecting an eGPU like Gigabyte Aorus 1070 but I am assuming I would have to disable the built-in Quadro card for 1070 to be utilized? How do I do that, disable it from device manager->Display Driver->Driver->Disable or is there a better way?
@mambo99, at this time, only the 15" Macbook Pro has TB3-CPU architecture. All other notebooks, including 13" Macbook Pro are using TB3-PCH architecture. As Intel rolls out royalty-free and on-die Thunderbolt in subsequent CPUs that may change. The E5480 and ZBooks use 4-lane TB3 and make excellent TB3 candidate systems. See other candidates here.
@MEJazz, to disable the M2000M, go to Device Manager->View->Devices by connection. Find the M2000M dGPU then disable the PCIe port directly above it. The M2000M will disappear, you can uninstall the Quadro drivers and install the Geforce GTX1070 drivers without any conflicts.
Can't i keep the Quadro drivers, I'd like to be able to switch between the two. Hopefully once the card is disabled the drivers won't be used. In other words the GeForce and Quadro drivers would co-exist and get utilized depending on which card is active.