Hi, this is not really an issue. I want to check if i have figured out right.
We are seeing a subtle performance difference since updating to UE5.7 (from UE5.5)
From what i have seen, the overall performance cost of Lumen is reduced. That is a great news.
However, while we were going to gain performance by turning off r.Lumen.HardwareRayTracing (HWRT),
in 5.7 turning off HWRT doesn’t give much performance benefit as before, or even consumes more depending on content setup.
I have tested it on vanilla Unreal 5.5 and 5.7.
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In attached screenshot, 5.7 wins in both cases, but in our content setup 5.7 loses slightly when HWRT is off.
If I figured out right, it is a desirable change, but as we were just going to turn off r.Lumen.HardwareRayTracing for performance reason, it is a bit surprise for us.
So, I am asking if what i have found is actually intended (not like a mistake in my testing content setup).
I just need to explain to our artists, and revise optimization plan according to new change. 
In addition, If there is new scalability options that worth trying regarding Lumen, could you provide them?
Thanks 
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Hi there,
The numbers you are seeing are correct. We have been making significant performance improvements to the HWRT code path for Lumen, and we aim to make it the default path going forward. Therefore, we actually recommend people use HWRT for Lumen over the software ray tracing path. We will be updating the Lumen Performance guide with the 5.8 release, so please check there for the new scalability settings once it’s out. I hope that helps, but please let me know in case you have any further questions.
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Ok, no problem! I am going to close out this ticket now, since your questions have been answered. Please open a new ticket if you have any follow-ups.
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Ok, now I see there are tons of changes in HWRT, from low level API to the acceleration data structure.
I will wait for the new performance guide.
Beside Lumen, is there anything that might cost more GPU power for material evaluation and lighting?
Unlike the screenshot attached above, In our content setup 5.7 is a bit slower without HWRT.
I initially suspected Lumen’s software path became slower, but now it looks like Lumen is not guilty, there are other passes that might become heavier.
In a quick glance, ProfileGPU reports heavier deferred lighting, but I don’t see a significant code change except Substrate path, while we don’t use it (r.Substrate=0)
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Ah, never mind.
It was DLSS that cost extra GPU time on our side.
Also, i found that new GPU profiler is introduced, so that explains whatever difference in ProfileGPU or Stat GPU items.
So the noticeable performance change in Unreal (from 5.5 -> 5.7) is in Lumen’s hardware RT path, which is faster now. No more mystery on our side.
Thanks a lot!
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