H2D bandwidth 15% lower than expected with 12th gen Yoga 9i + Breakaway Box 750
- Yoga 9i
- i7 1260p
- Two thunderbolt 4 ports
- HWINFO64 reports those ports are using a JHL6340 controller, PCIE 3.0 4x, Max link speed 8.0 GT/s, Current link speed 2.5 GT/s
- Sonnet Breakaway Box 750 (not the ex variant)
- According to https://egpu.io/best-egpu-buyers-guide/ it uses a JHL7440 controller
- 40Gbps Thunderbolt 3 cable (the one that came with the Breakaway Box 750)
- RTX 3080 10GB
- Outputting to external display via Displayport output of RTX 3080. Yoga 9i is closed and internal display is disabled
CUDA-Z reports only 2130 MiB/s of H2D bandwidth (and 2750 MiB/s of D2H bandwidth). Based on data points like https://egpu.io/forums/builds/2021-14-lenovo-yoga-slim-7-11th-4c-gigabyte-aorus-1660-ti-tb4-cooler-master-eg200-win10-20h2/, it's possible to achieve 2450 MiB/s (15% higher) H2D bandwidth with a JHL7440 eGPU enclosure and an nvidia GPU. This guy ( https://egpu.io/forums/builds/2021-13-dell-xps-13-9310-11th4cg-rtx-3060-32gbps-tb3-sonnet-breakaway-box-750ex-win10/) has achieved 2365 MiB/s H2D bandwidth with the JHL7440 Breakaway Box 750 ex (which includes a USB hub, which may be reducing his bandwidth a bit) with an nvidia GPU. Even with DSL6540 eGPU setups (like the Razer Core X), people commonly achieve 2260 MiB/s H2D bandwidth (e.g. https://egpu.io/forums/builds/2020-14-acer-swift-3-iris-plus-g7-10th4cg-rtx-2070-32gbps-tb3-razer-core-x-win10/), which is more than I'm getting. (My understanding is that DSL6540 eGPU enclosures are capable of ~15% lower bandwidth as compared to JHL7440) enclosures.
Any ideas what's going on? Anything I can try to achieve higher (ideally ~2450 MiB/s) H2D bandwidth? Could the problem be the JHL6340 controller that is behind my laptop's Thunderbolt 4 ports? JHL6340 seems sort of old (and is classified as a Thunderbolt 3 controller) but my laptop advertises Thunderbolt 4 ports.
Here is what HWINFO64 shows when the eGPU is connected:
Here is what HWINFO64 shows when the eGPU is disconnected:
Is it possible that the JHL6340 I see is actually from the Breakaway Box 750? And HWINFO64 doesn't list any Thunderbolt controller for my laptop, because in Alder Lake P thunderbolt has been moved from the chipset and into the CPU? If the Breakaway Box 750 has a JHL6340 and not a JHL7440, then maybe that's the reason my H2D bandwidth is low. On the other hand, according to https://egpu.io/wikingoo-egpu-review-diy-thunderbolt-3-external-gpu/, it's possible to get 2450 MiB/s H2D with a JHL6340 Wikingoo eGPU.
Yes, there appears to be some misinfo about what is advertised (JHL7440) and what actual TB controller is (JHL6340) in the Sonnet Breakaway Box 750 series: