- May 28, 2009
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We have seen overclocks hit a wall at around 5 GHz, but really it's just the tail end of rather extreme cooling solutions. I was surprised to find out that how we get there isn't just a steady climb. Meanwhile Intel's ultra mobile devices turbo up to around 3 GHz which, as it turns out, may not be just an arbitrary number.
So I probed and recorded the full voltage range of my 22nm Haswell-Refresh Pentium Anniversary Edition G3258. But really it is representative of all Haswell CPUs, just move it around a little or bend it a bit if you are on a stock cooler.
At first glance this is just a steady increase, meaning ramping up the cpu frequency in 100 MHz steps always requires Vcore to be raised. But a closer look reveals that there are two pieces to this graph, one that is almost completely linear and a second one that visibly curves upwards.
I tried to highlight the point where the curvatures kicks off, but it's kind of hard to pinpoint in this representation.
So to make this threshold more pronounced I plotted the voltage difference between two multipliers (AKA differetial or delta). Unfortunately this also makes measurement inaccuracies more pronounced. Also added some temperature (Tmax) data.
Because it is an numeric approximation of a derivation of the original voltage curve, linear parts become flat and parabolic-ally curved parts become linear.
More importantly though, the two pieces of the voltage delta show very different trends. Stock frequencies up to 3.2 GHz show that it takes on average ~ 17 mV to reach the next step. This voltage basically compensates for increased frequency, as temperatures only slowly creep upwards. Beyond 3.3 GHz however voltage jumps increase, to the point where most of the voltage serves to stabilize and compensate for the now much higher and faster climibing temps.
CPUs really hit a wall around 3.3 GHz not 5 GHz, about where the two trend lines intersect. What happens then is that desktop makers keep bashing their heads against this thermal wall with increasingly ludicrous cooling solutions and diminishing returns that allow for a rather unimpressive ~1.5 GHz of headway!
What I like to know is: What do you think happens inside the CPU around 3.3 GHz that sets off the sudden rise of temps?
Does this threshold or wall move when going from one node process to the next? If it does, which way did it shift for 14nm Skylake?
So I probed and recorded the full voltage range of my 22nm Haswell-Refresh Pentium Anniversary Edition G3258. But really it is representative of all Haswell CPUs, just move it around a little or bend it a bit if you are on a stock cooler.
At first glance this is just a steady increase, meaning ramping up the cpu frequency in 100 MHz steps always requires Vcore to be raised. But a closer look reveals that there are two pieces to this graph, one that is almost completely linear and a second one that visibly curves upwards.
I tried to highlight the point where the curvatures kicks off, but it's kind of hard to pinpoint in this representation.
So to make this threshold more pronounced I plotted the voltage difference between two multipliers (AKA differetial or delta). Unfortunately this also makes measurement inaccuracies more pronounced. Also added some temperature (Tmax) data.
Because it is an numeric approximation of a derivation of the original voltage curve, linear parts become flat and parabolic-ally curved parts become linear.
More importantly though, the two pieces of the voltage delta show very different trends. Stock frequencies up to 3.2 GHz show that it takes on average ~ 17 mV to reach the next step. This voltage basically compensates for increased frequency, as temperatures only slowly creep upwards. Beyond 3.3 GHz however voltage jumps increase, to the point where most of the voltage serves to stabilize and compensate for the now much higher and faster climibing temps.
CPUs really hit a wall around 3.3 GHz not 5 GHz, about where the two trend lines intersect. What happens then is that desktop makers keep bashing their heads against this thermal wall with increasingly ludicrous cooling solutions and diminishing returns that allow for a rather unimpressive ~1.5 GHz of headway!
What I like to know is: What do you think happens inside the CPU around 3.3 GHz that sets off the sudden rise of temps?
Does this threshold or wall move when going from one node process to the next? If it does, which way did it shift for 14nm Skylake?