By: David Kanter (dkanter.delete@this.realworldtech.com), May 17, 2013 8:12 am
Room: Moderated Discussions
Ashraf Eassa (aeassa.delete@this.gmail.com) on May 15, 2013 11:59 am wrote:
> Hi everybody,
>
> I've been lurking for years, but the time has come when I would really love to pick the brains of
> the experts we have here. From my understanding, Atom is a much narrower design than Krait, Cortex
> A15 and others, and yet, in many benchmarks the older Saltwell core holds its own against even Krait
> in both FPU/INT, and against A15 in Linux integer benchmarks (but it gets decimated in FPU).
> So, my question is, how do I think about "Silvermont" competitive position against a fairly
> beefy modern ARM design such as the Cortex A15? From a high level perspective, it looks
> like on a per-clock basis it should be no contest - A15 is wider and more aggressive.
> But Intel is claiming that Silvermont is as fast as A15 on a per-clock basis.
I don't think anyone at Intel has ever made claims on a per-clock basis. They have made comparisons on a per-unit-of-power basis.
> A couple of questions then:
>
> 1. How can a narrower design pull this off?
First, issue width and actual IPC are only loosely related.
I'd suggest you look at my article on silvermont and other architectures. I spend a tremendous amount of time discussing all the details including techniques which boost IPC without increasing issue width. My Haswell article is probably also quite informative in that regard.
> 2. Is this likely to be integer only as A15 includes FMAC instructions,
> which in the right cases double FPU performance?
Intel isn't really aiming for FP performance with Saltwell or Silvermont, so it's unlikely that they will do that well compared to the A15. Although, Intel's vector implementation seems much more robust than the A15 Neon.
DK
> Hi everybody,
>
> I've been lurking for years, but the time has come when I would really love to pick the brains of
> the experts we have here. From my understanding, Atom is a much narrower design than Krait, Cortex
> A15 and others, and yet, in many benchmarks the older Saltwell core holds its own against even Krait
> in both FPU/INT, and against A15 in Linux integer benchmarks (but it gets decimated in FPU).
> So, my question is, how do I think about "Silvermont" competitive position against a fairly
> beefy modern ARM design such as the Cortex A15? From a high level perspective, it looks
> like on a per-clock basis it should be no contest - A15 is wider and more aggressive.
> But Intel is claiming that Silvermont is as fast as A15 on a per-clock basis.
I don't think anyone at Intel has ever made claims on a per-clock basis. They have made comparisons on a per-unit-of-power basis.
> A couple of questions then:
>
> 1. How can a narrower design pull this off?
First, issue width and actual IPC are only loosely related.
I'd suggest you look at my article on silvermont and other architectures. I spend a tremendous amount of time discussing all the details including techniques which boost IPC without increasing issue width. My Haswell article is probably also quite informative in that regard.
> 2. Is this likely to be integer only as A15 includes FMAC instructions,
> which in the right cases double FPU performance?
Intel isn't really aiming for FP performance with Saltwell or Silvermont, so it's unlikely that they will do that well compared to the A15. Although, Intel's vector implementation seems much more robust than the A15 Neon.
DK
