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.

Thunderbolt 3 host, Dell Precision 7520 review

 

Introduction

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.

Computer Type Advantage Disadvantage
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.

 

Hardware Specifics

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 eGPUPrecision 7520 Internal DisplayPrecision 7520 External DisplayZ170 Test Bench
Unigine Valley47.0 FPS49.2 FPS50.8 FPS
Unigine Heaven47.1 FPS48.7 FPS49.2 FPS
Unigine Superposition54.2 FPS57.6 FPS55.3 FPS
3DMark Time Spy26.7 FPS27.6 FPS27.4 FPS
3DMark Fire Strike56.4 FPS57.1 FPS57.0 FPS
Rise of the Tomb Raider55.7 FPS57.2 FPS58.0 FPS
Tom Clancy's Ghost Recon39.3 FPS43.1 FPS41.5 FPS
Shadow of Mordor69.7 FPS87.0 FPS83.3 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.

 

Conclusion

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.

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