thicc_girls_are_teh_best
Member
Posted this in another thread but it got locked before I could hit the reply button lol. Anyway, I was responding to
ethomaz
who brought up an interesting point regarding power-to-frequency scaling on RDNA1 and speculated possible efficiency gains in that regard with RDNA2. Their reply was the following:
Now, I was compelled to respond in particular to the last part, because IMHO I don't know if the gains are THAT vast. There's some other factors to consider here. Tried keeping it brief but this is essentially what I feel on the matter.
Anyway, just wanted to see what and how others felt about this particular aspect of things.
Nothing changed just the interpretation of the results.
RDNA has a "sweet" clock spot where the increase in clock start to have disproportionately increase in performance... that is around 1900Mhz or so... when you go over that says 10% your increase in performance is just 3-5%.
But when you do that in lower clocks like 1500Mhz with 10% increase in clock will turn out in 9-10% increase in performance because it didn't reach the "sweet" spot for performance start to not scale at the same rate than clock.
RDNA 2 increase that "sweet" spot to another level... PS5 running at 2.2Ghz tells us that RDNA now can reach these clocks with 40CUs at good performance scale different from RDNA that couldn't.
Now, I was compelled to respond in particular to the last part, because IMHO I don't know if the gains are THAT vast. There's some other factors to consider here. Tried keeping it brief but this is essentially what I feel on the matter.
Dunno how true of a case this actually this. First off, we know RDNA2 is a dual-process initiative: 7nm DUV enhanced, and 7nm EUV. We know the consoles are on 7nm DUV enhanced. We also know there have been persistent rumors for about a year now regarding PS5 cooling, both in terms of outright rumors (not getting into that "recent" one which has a questionable source), and just inference from looking at the design itself.
RDNA1's sweetspot is between 1700 MHz to 1800 MHz for power-to-performance. While AMD's mentioned 50% PPW gains in RDNA2 over RDNA1, we don't know on which process they are specifying this, and there's a chance there's some slight embellishment to that figure, because these kind of companies (AMD, Nvidia, Intel, Sony, Microsoft etc.) do that all the time.
If I were being generous, RDNA2's sweetspot probably has an upper limit of around 2 GHz, and that's with sufficient amounts of cooling being provided (comparable to an upper-end PC GPU card most likely). We can look at the XSX and see that even with "just" 1825 MHz GPU clock, that thing has a massive heat sink and a pretty elaborate cooling setup of its own. And, again, it's the same process node as PS5's GPU.
I'd expect PS5's cooling (in terms of sheer amount) to be around that level, because even if the GPU is smaller that's being offset by the higher maximum clocks. But I would still say that for an RDNA2 DUV enhanced chip, PS5's GPU clock is most likely definitely pushing beyond the sweetspot. What we need to know now, is if the frequency-to-performance gain ratio has improved significantly from RDNA1 tech, because those required a vast amount of additional power beyond their sweetspot for marginal frequency gains.
Going by Cerny's own words, a 10% reduction in power will result in a 2% drop in GPU and CPU frequency. So that's a 5:1 ratio, essentially, of power-to-frequency. I don't know how that compares to RDNA1 tech, but I'd picture that you'd want a smaller ratio than that. That amount he refers to could be referring to a clock range beyond the RDNA2 sweetspot, as well, because I would assume with overall architectural and node efficiency gains you wouldn't need a 5:1 ratio at sweetspot ranges (or certainly anything lower than that).
Oh well; we're going to see eventually once Sony does that cooling teardown (I'm assuming with Digital Foundry and maybe a few other tech channels as well). Ultimately this isn't me speaking to anything in the article, not agreeing or disagreeing with anything there. But I just wanted to touch on the power, heating, and cooling aspects of PS5 and RDNA2, just some personal speculation.
Anyway, just wanted to see what and how others felt about this particular aspect of things.