By: Joel (joel.hruska.delete@this.gmail.com), April 29, 2015 12:26 pm
Room: Moderated Discussions
David Hess (davidwhess.delete@this.gmail.com) on April 29, 2015 8:38 am wrote:
> Pierre (Boutoukoat.delete@this.yahoo.fr) on April 29, 2015 4:38 am wrote:
> >
> > Dissipated power is O(frequency) and O(squared voltage). The article mention the voltage could be reduced
> > by 200 millivolts, e.g. go from 0.9 to 0.7 volts. This mean a reduction of power of 40%, and in layman
> > terms, 40% more battery life on a processor 4 times cheaper. Reasoning at constant power and ignoring
> > o a lot of details, frequency could increase by 40% if voltage goes from 0.9V to 0.7V. However, most of
> > the perceived performance out of a processor comes from memory speed (unchanged ...) , parallelism and
> > integration of co-processors like GPU and NICs (more transistors), and software benchmarks.
>
> Power density is also becoming a limiting factor. Heat pipes helped here however they have their own
> hard power density limits and now require heat spreaders between the CPU and evaporator. If you reduce
> the power by 40% but have the same number of transistors in 1/4 of the area, then the power density
> increases by 160%. Raising the frequency by 40% and keeping the power constant would increase the power
> density by 300%. Either the junction to case thermal resistance has to be lowered (diamond?) or a higher
> junction temperature is needed which will adversely affect reliability and leakage.
>
> > For the last 10 years, frequency of desktops for gamers has not increased (peak around 4 Ghz on
> > the most expensive Intel CPUs). It looks unlikely to change in the near future, and the trend
> > to add more cores will continue. I hope this helps to answer your obsolete question "how faster
> > ?" typical from the 90's. Right questions now are "how cheaper ?" , "how longer ?" ...
>
> AMDs current CPUs top out in the 4 GHz range as well. Adding more cores to take advantage of higher
> density processes is going to run up against power density limits and most applications including
> games cannot take advantage of more cores anyway. Do any games make use of more than 2 cores?
>
Yes. There are many modern titles that can make some use of up to four cores, though not much scales past that. DX12 is expected to vastly improve this scenario; it allows for effective multi-threading in ways that DX11 never supported.
Early DX12 games and applications can take full advantage of all eight cores on a Haswell-E system and see performance gains from doing so.
> Pierre (Boutoukoat.delete@this.yahoo.fr) on April 29, 2015 4:38 am wrote:
> >
> > Dissipated power is O(frequency) and O(squared voltage). The article mention the voltage could be reduced
> > by 200 millivolts, e.g. go from 0.9 to 0.7 volts. This mean a reduction of power of 40%, and in layman
> > terms, 40% more battery life on a processor 4 times cheaper. Reasoning at constant power and ignoring
> > o a lot of details, frequency could increase by 40% if voltage goes from 0.9V to 0.7V. However, most of
> > the perceived performance out of a processor comes from memory speed (unchanged ...) , parallelism and
> > integration of co-processors like GPU and NICs (more transistors), and software benchmarks.
>
> Power density is also becoming a limiting factor. Heat pipes helped here however they have their own
> hard power density limits and now require heat spreaders between the CPU and evaporator. If you reduce
> the power by 40% but have the same number of transistors in 1/4 of the area, then the power density
> increases by 160%. Raising the frequency by 40% and keeping the power constant would increase the power
> density by 300%. Either the junction to case thermal resistance has to be lowered (diamond?) or a higher
> junction temperature is needed which will adversely affect reliability and leakage.
>
> > For the last 10 years, frequency of desktops for gamers has not increased (peak around 4 Ghz on
> > the most expensive Intel CPUs). It looks unlikely to change in the near future, and the trend
> > to add more cores will continue. I hope this helps to answer your obsolete question "how faster
> > ?" typical from the 90's. Right questions now are "how cheaper ?" , "how longer ?" ...
>
> AMDs current CPUs top out in the 4 GHz range as well. Adding more cores to take advantage of higher
> density processes is going to run up against power density limits and most applications including
> games cannot take advantage of more cores anyway. Do any games make use of more than 2 cores?
>
Yes. There are many modern titles that can make some use of up to four cores, though not much scales past that. DX12 is expected to vastly improve this scenario; it allows for effective multi-threading in ways that DX11 never supported.
Early DX12 games and applications can take full advantage of all eight cores on a Haswell-E system and see performance gains from doing so.
