I have been using my r9 380x on linux for quite a while now. But since a bit ago its performance seems to be getting worse (random stutters, low framerate). I was thinking about doing a repaste. But before I was gonna do that. I thought I'd run some tests, and I got some... confusing results.

I started by trying to get my gpu temperature, which, in my case meant running: sudo sensors-detect this tool seemed to suggest it had found a temperature sensors in my gpu:
AMD Family 17h thermal sensors...                           Success!
    (driver `k10temp')
next, I ran: sensors
Which gave me the following info:
nvme-pci-0900
Adapter: PCI adapter
Composite:    +42.9°C  (low  = -273.1°C, high = +109.8°C)
                       (crit = +129.8°C)
Sensor 2:     +62.9°C  (low  = -273.1°C, high = -273.1°C)

k10temp-pci-00c3
Adapter: PCI adapter
Tctl:         +37.4°C  
From what I saw from the sensors-detect output, I kinda assumed that k10temp-pci-00c3 would be my gpu temp. But after running furmark for a while, I got the following readings:
nvme-pci-0900
Adapter: PCI adapter
Composite:    +48.9°C  (low  = -273.1°C, high = +109.8°C)
                       (crit = +129.8°C)
Sensor 2:     +62.9°C  (low  = -273.1°C, high = -273.1°C)

k10temp-pci-00c3
Adapter: PCI adapter
Tctl:         +38.2°C  
And, well, 1°C after like 20 min of furmark doesn't seem right. The only temp that really went up was the one labeled: "composite". And, 48.9°C still sounds quite low. But the thing is, I looked at my gpu, and, my gpu fans aren't even spinning (they do some spinning when I boot up the computer, so I assume the fans work at least), so, it is almost like the gpu thinks it is actually not getting much hotter.

So, all of this just left me with a bunch of questions. Am I looking at the right sensors? If not, how do I get a readout for the right sensors? And if I am looking at the right sensors, why is the temperature barely going up?
It is like my gpu has some thermal cap, which makes it throttle super hard at 49 degrees without even bothering to turn on the fans. But that just seems strange. I have never even touched stuff like the fan curves and other gpu settings from linux, also, these super low framerates I have been getting seem to be a recent thing, so you'd think something must have changed.