By: Exophase (exophase.delete@this.gmail.com), June 3, 2013 12:02 pm
Room: Moderated Discussions
Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on June 3, 2013 10:52 am wrote:
> On the other hand the only A15 implementation available until a few weeks ago
> (Exynos 5250) is unlikely to be indicative of all A15 implementations.
No, but it's better than the Silvermont hardware ARM has access to, which is nothing.
> If you compare quad A7 vs dual Atom then yes that appears quite possible. Note the A7 does currently
> clock up to 1.4GHz and is only a little slower than A9 due to a much better memory system.
>
I've seen A7 positioned as ~25% slower than A9 at the same clocks, and a limited amount of benchmark data that supports this. Is there anything better about the memory system outside of the lower latency L2 cache? And where does it clock at 1.4GHz? ARM only says "> 1GHz." Exynos 5410 has a limit of 1.2GHz. Other SoCs I know of are 1GHz.
> According to Samsungs ISSC graph, a quad A7 at 1.2GHz uses ~500mW, or just ~125mW per core.
>
The numbers I gave are also from Samsung (in their kernel source) so the two are in disagreement. It could be that those numbers are for a worse bin.
> Unless you use extra cores of course. Assuming a 1.2GHz A7 is about as fast as a 1GHz
> Atom, a quad A7 at 1.2GHz should be able to match dual Atom with hyperthreading at 2GHz.
> Extrapolating your Atom power figures, Atom would use ~1170mW per core at 2GHz. So it
> would be 2343mW vs 500mW, close to a factor of 5 as claimed by the ARM slide.
>
Aside from that this would only apply to code that scales perfectly with core count it also sounds like it's vastly undershooting the benefit of HT. It's common for it to improve performance on Atom by 40, even 50%. That'd bring the needed clocks for Atom as low as 1.4GHz, which grossly changes the comparison.
> On the other hand the only A15 implementation available until a few weeks ago
> (Exynos 5250) is unlikely to be indicative of all A15 implementations.
No, but it's better than the Silvermont hardware ARM has access to, which is nothing.
> If you compare quad A7 vs dual Atom then yes that appears quite possible. Note the A7 does currently
> clock up to 1.4GHz and is only a little slower than A9 due to a much better memory system.
>
I've seen A7 positioned as ~25% slower than A9 at the same clocks, and a limited amount of benchmark data that supports this. Is there anything better about the memory system outside of the lower latency L2 cache? And where does it clock at 1.4GHz? ARM only says "> 1GHz." Exynos 5410 has a limit of 1.2GHz. Other SoCs I know of are 1GHz.
> According to Samsungs ISSC graph, a quad A7 at 1.2GHz uses ~500mW, or just ~125mW per core.
>
The numbers I gave are also from Samsung (in their kernel source) so the two are in disagreement. It could be that those numbers are for a worse bin.
> Unless you use extra cores of course. Assuming a 1.2GHz A7 is about as fast as a 1GHz
> Atom, a quad A7 at 1.2GHz should be able to match dual Atom with hyperthreading at 2GHz.
> Extrapolating your Atom power figures, Atom would use ~1170mW per core at 2GHz. So it
> would be 2343mW vs 500mW, close to a factor of 5 as claimed by the ARM slide.
>
Aside from that this would only apply to code that scales perfectly with core count it also sounds like it's vastly undershooting the benefit of HT. It's common for it to improve performance on Atom by 40, even 50%. That'd bring the needed clocks for Atom as low as 1.4GHz, which grossly changes the comparison.