How is AMD GPU clock speed determined?

[orangecat]

So on my GTX 970 there is a set of clock speeds the GPU can operate at. For example it will run from 135Mhz up to 1392Mhz but theres fixed steps in between. I was using my dads RX460 because I needed a GPU that my power supply could handle until I had the time to send it in for RMA and I noticed the clock speeds were always changing and sometimes changed less than 1 full megahertz. The clock speed topped out at 1212Mhz but sometimes would also show up as 1219.5Mhz or something in GPU-Z. It seems like the AMD GPU clock is generated differently that how Nvidia does it and I'm curious to know how it's done. It seems like the clock speed is programmable to a very fine degree. It also jumps around allot during load where as my GTX 970 basically just locks to it's highest sustainable frequency.

[Mr.Meerkat]

Okay, my experience with 2 290Xs, multiple 7950s, a 7990, a RX470 and a Fury...specifically the RX470...

 

An AMD GPU will  typically boost/clock at the maximum speed assuming these 2 conditions are met:

- Its not exceeding the power limit/voltage

- It is not hitting/surpassing the 'safe' maximum temperature (i.e. target temp)

 

Generally the cause for a stock GPU's clock speed to bounce around is its surpassing or hitting the target temp meaning its clocking down. To fix this, go into wattman, crank target up to 80C~ [depends on what you feel comfortable with] and typically it will stabilize and maintain max clocks.

 

Ah fun times when every single time I update my drivers for my RX470, it would be unable to maintain 1270MHz as it was consistently hitting the 65C limit, clocking down to as low as 1100MHz~  

 

[DragonTamer1]

I'm not entirely sure why AMD does it, but it is a common thing with their cards apparently. When I bought my 480 I thought it was defective because of this but I've never had an issue.

 

The only reason I can think of is that the card is trying to maintain its highest power efficiency while delivering the performance it needs by not boosting up too high. I'm not an expert though, there is probably something much more complex going on under the hood.

 

Edit: would it happen to look like this?

[Mr.Meerkat]

@DragonTamer1 What are your temperatures? My RX470 looked like that until I raised the target temp way past the temperature it hit underload (i.e. it was hitting 70C~ underload, raising target to 80C~ allowed it to maintain both stock 1270MHz and OCed 1300MHz at all times)

 

[DragonTamer1]

4 hours ago, Mr.Meerkat said:

@DragonTamer1 What are your temperatures? My RX470 looked like that until I raised the target temp way past the temperature it hit underload (i.e. it was hitting 70C~ underload, raising target to 80C~ allowed it to maintain both stock 1270MHz and OCed 1300MHz at all times)

 

Max temp that I've seen during stress test is 73*C. My power limit is +50% temp limit is 95*C and it is undervolted by 48mV with a boost to core speeds of 32MHz (1310). It is worth noting that that the GPU is at idle in that screen shot.