Thunderbolt eGPU bandwidth limit explained | RTX 4090 + 13700H

if you've ever been interested in connecting  an external graphics card most of you probably   know about the issues they have related to the  bandwidth limit up to 40 Gbps we've heard this   phrase a lot but I was wondering what bandwidth  limitation actually is and how exactly does it   affect GPU performance is it in the number of  frames it can send to the monitor maybe the   limitation relates to the number of Tflops  processed does the performance also depends   on USB devices connected to the eGPU as some  of you mentioned in the comments I've read a   lot of Articles and documentation did a lot  of benchmarks and even contacted Thunderbolt   directly for some clarification so now I'm ready  to answer those questions and to ensure that the   technical side of the test is accurate as  possible I'll connect a top tier graphics   card to quite powerful laptop this time I bought  a new gigabyte AERO it comes equipped with one of   the latest Intel CPUs 13700H which has 14 cores  20 threads and 16 GB of LPDDR5 memory and even   a discrete RTX 4050 it has a stylish design  without overwhelming RGB lightning it's slim   and lightweight and it's packed into a compact  chassis with a stunning 14' OLED display at 90   HZ refresh rate and most importantly it has a  Thunderbolt 4 Port which we need for our eGPU   if you're interested in which eGPU enclosure  I'll be using how it works and how to set it   up I have already made a video about it and you  can find it in the suggested videos while I set   up everything it's essential to understand the  theory theoretical cable bandwidth is up to 40   Gbps but when connecting PCI devices such  as eGPU it's allocated to 4 PCIe lines 3.0   or in other words 32 Gbps despite having the  same bandwidth between the Thunderbolt 3 and   4 versions Thunderbolt 3 has lower minimum PCIe  data requirements this means it can operate at   speeds from 16 to 32 Gbps and every eGPU enclosure  based on Thunderbolt 3 if you are curious about   USB4 version speed it uses Thunderbolt 3 standards  after all the cable version is not the only factor   that determines speed another factor is the  Thunderbolt controllers that are included in   every device this controller is responsible for  the feature set that will be available on your   device for example I found out that my laptop's  Thunderbolt doesn't support charging so I always   had to connect an additional cable for it as far  as I understood existing eGPU controllers are   cap capable of delivering 22-24 Gbps of bandwidth  according to Aida GPU Benchmark and the remaining   bandwidth is probably for the reverse video  signal in case of using the built-in monitor   of the laptop and USB devices so what is this  bandwidth used for to explain this let's take a   simplified look at how frames are generated for  games CPU calculates the logic creates object   geometry and sends instruction to the graphics  card through the PCIe lines which have a variant   bandwidth depending on the version meanwhile the  GPU takes data from the CPU and performs Graphics   related calculations this includes rendering 3D  objects applying shaders calculating lighting   and effects afterwards it creates a frame that  sends to the monitor therefore if CPU generates   instructions for 100 frames per second and the  GPU can handle only 70 GPU becomes a bottleneck   and you'll see only 70 frames per second and vice  versa in case of eGPU everything works similarly   but instead of PCIe lines we have a Thunderbolt  connection which may not have enough bandwidth to   transfer CPU instructions to the GPU therefore if  you use the laptop's built-in monitor the finished   frames needs to be sent back and use already  limited bandwidth and impact performance even   more with the theory covered it's time to move  on to the tests we'll be using an RTX 4090 and   I am interested to see the percentage of its  utilization so all tests will be done in 4k to   push GPU to the limits I also want to find out  what a combination of a powerful laptop with a   high-end GPU is capable of it is important to note  that you shouldn't focus only on the percentage of   GPU utilization on the chart it looks inaccurate  when RTX 4090 is running at 90% of utilization   it cannot consume only 200 watts and deliver such  low frame rate since it typically consumes around   420 Watts under full load occasionally going up  to 450 wats so in games where power consumption   rises above 300 wats we can see an excellent  performance and we should pay more attention   to this indicator if it's at 200 Watts it means  that the graphics card is roughly loaded at about 50% I've noticed a tendency where games that are  more CPU demanding tend to put a minimal load on   the GPU this might be due to the large number of  instructions the TPU can send to the graphics card   quickly enough due to the limited bandwidth the  Battlefield had a lot of stuttering and I'm sure   it's not CPU bottleneck as the gameplay was even  more stable on the discrete RTX 4050 at the same   time games like rocket League can deliver over  600 frames on minimum settings and over 300 on Max settings in DEATHLOOP FPS varies from 50 to 100   depending on where you look at and  this is unusual behavior for this game and Days Gone showed the best results so far God of War also performed well but  there was likely a CPU bottleneck as FPS   didn't change much with changing DLSS  from Ultra-performance to disabling it completely and every other game that I've tested  has shown no problems only insufficient GPU utilization regarding the USB connection in my first  eGPU video I connected an SSD with games   to the eGPU so I wouldn't have to store them  on the laptop storage this way you connect one   cable and you have both the graphics card  and your game library but few people wrote   to me that this negatively affects bandwidth  this seemed unlikely because SSD's are barely   stressed during gaming but I tested it by  running a game from an external SSD connected   to the eGPU and from the laptop's internal  storage and there was no difference at all   to make this test even more complex I started  copying files from the SSD to the laptop and   even that didn't affect performance but why  it's likely because part of the bandwidth is   reserved for this on the table controller  of the eGPU so you can use SSD's this way   also I tried to connect VR headset directly  to the eGPU and it worked with no issues at all after all these tests I came to the conclusion  that there is no recommend GPU as an external   graphics card I often heard the phrase that there  is no point in buying anything more powerful than   RTX 3060 and perhaps in the past that was the  case maybe it was assumed with a laptop having   let's say 4 cores 8 threads so your CPU will be  a bottleneck but times are changing my laptop now   has 14 cores 20 threads can work at 5 GHz and  it's more than capable of working with serious   graphics cards as demonstrated in case of Days  Gone we can see an excellent result that an RTX   3060 couldn't come close to achieving for  instance here are results with a built-in   RTX 4050 but anyway we shouldn't forget about  examples where high-end GPU performed poorly   in CPU demanding games but I'm not sure if this  will be a problem for those who just want to use   opportunity to play on their older laptops with  budget graphics cards in this scenario even if   there is no bandwidth issue the FPS wouldn't  go any higher so I wouldn't bury the idea of   eGPU why not just buy a gaming laptop well then  it won't be as light and portable they can be   noisy under load and they're expensive this laptop  cannot be called cheap either and I really wanted   to keep it instead of my PC however ever this  laptop make noise even when you use a browser   and to avoid that I had to change power settings  to power saver every time manually after using a   MacBook which works most of the time without the  fans it's hard for me to accept this moreover it   was behaving unstable after my laptop went to  sleep or was restarted I had to reconnect the   cable from the eGPU or external SSD every time  and the lack of the ability to charge the laptop   via Thunderbolt cable this created a terrible  user experience to me although it was perfect   on paper but I returned it to the store I didn't  face such issues with the Thunderbolt connection   on my Lenovo office laptop maybe because of a  better Thunderbolt controller I don't know by   the way the first devices with Thunderbolt 5  will be releasing soon which looks promising   I'll wait for more power efficient laptop  with Thunderbolt 5 and proper cooling for   now I'll go back to my desktop PC that has a  Thunderbolt Port guess what I want to test now

Channel: Try Some Tech

Views: 62,349

Keywords: eGPU, external GPU, external graphics, eGPU comparison, PCIe bandwidth, EGPU, nvidia, thunderbolt 3, external gpu for laptop, RTX 4090, intel, egpu th3p4g3 review 4090, external graphics card, best external gpu 2023, TH3P4G3, business laptop gaming, aliexpress, aliexpress egpu, gaming laptop, thunderbolt 4 egpu, thunderbolt 3 egpu, GIGABYTE AERO 14 OLED BMF, Thunderbolt explained, egpu bandwidth, Thunderbolt 4 egpu, 13700H, 40gbps, GPU Bottleneck, eGPU Setup, Tech Experiments

Id: _UE_2NyaAas

Length: 10min 32sec (632 seconds)

Published: Mon Oct 30 2023