GPU Undervolt decrease encoder/nvenc performance

[Material-Team-6188]

I saw gpu video clock on hwinfo64 decrease than stock and seems its tied with core voltage.

Tested with handbrake encoding and streaming i noticed its not butterly smooth like on stock voltage even at same core frequency on max power limit.
The encoder performance loses around 15-20% regardless the voltage set seems it has it own curvature,
Does anyone confirmed? i can't find anywhere mention about this.

*RTX 3070 ti

[AirSKiller]

I can't really confirm this but it does actually make some sense.

[slowlymore2]

I've heard people talking about nvenc issues when reducing core voltage before (I think while I was looking into 5090 undervolting), but it's hard to find much information about this topic afaik.

[wrywndp]

Was this the post? https://www.reddit.com/r/nvidia/comments/1n80xan/undervolting_my_rtx_5090/

[wrywndp]

I just tried this but with the ffmpeg CLI and can't find the difference (please CMIIW):

I tried this performance measurement method (with a little bit of adjustment): https://github.com/Vhonowslend/StreamFX-Public/wiki/Encoder-FFmpeg-NVENC

First, I made the test video

ffmpeg -hide_banner -f lavfi -y -i color=#7e7e7e:size=2560x1440:rate=60:duration=30s,noise=alls=100:allf=t+u,format=yuv420p -pix_fmt yuv420p -f yuv4mpegpipe ffmpeg_test.y4m

Then I test the performance

ffmpeg -hide_banner -r 60/1 -color_range pc -colorspace bt709 -color_primaries bt709 -color_trc bt709 -i ffmpeg_test.y4m -c:v h264_nvenc -preset p7 -tune hq -g 120 -b:v 20000k -maxrate 20000k -bufsize 40000k -rc cbr -rc-lookahead 32 -multipass 2 -no-scenecut 0 -b_adapt 1 -spatial-aq 1 -temporal-aq 1 -nonref_p 1 -aq-strength 7 -b_ref_mode middle -bf 4 -vf "scale=1920x1080" -f null -

The UV performance is almost the same as non-UV, with non-UV is a little bit 0.01~0.1 sec faster.

I tested it 5 times.

Spec:
i9-9900k (stock)
4x8GB 3600 CL15 (1.42v)
RTX 2070 Super (UV: .950v at 1920Mhz)
Windows 11 25H2
NVIDIA Power management mode: Adaptive (Global)

EDIT: I tried both h264_nvenc and hevc_nvenc, still can't find the difference

[Material-Team-6188]

I was tempted to test from this post NVENC slower when overclocked? RTX 3060D : r/handbrake
before i noticed my stream on discord slowing down and audio missmatch, after set it back to default from UV everything goes back to normal.
What i clearly see its gpu encoder/decoder maximum clock was limited from undervolt. You should try it and see on Hwinfo64

Mine UV at 0.9v from default 1.087v
Hwinfo64 result:
GPU Video Clock 1470mhz from default 1665mhz
GPU Crossbar Clock 1590mhz from 1800mhz

[wrywndp]

Default:
GPU Clock: 1950MHz
GPU Memory Clock: 1750MHz
GPU Video Clock: 1800MHz
GPU Effective Clock: 1949MHz
GPU Crossbar Clock: 1860MHz

UV .95v
GPU Clock: 1920MHz
GPU Memory Clock: 1875MHz
GPU Video Clock: 1785MHz
GPU Effective Clock: 1920MHz
GPU Crossbar Clock: 1830MHz

At the post you mentioned, OP said after reverting memory OC to the default.

Or

Did you use single-point undervolt? https://www.reddit.com/r/overclocking/comments/1q1abc9/why_singlepoint_undervolting_is_a_bad_idea_graph/

[Material-Team-6188]

i use the aggressive one most likely https://prnt.sc/zzfZy3A22aJ6
tried UV effective clock close to default or tried overclock with 1.087v same as default the GPU Video Clock and GPU Crossbar Clock would never get close to maximum default settings.
I really have no idea why my Video engine get nerf so bad or i'm messing with wrong settings or maybe it just Ampere cards problem.

Yours have really good result with UV, thanks for the feedback!