By: Wilco (Wilco.Dijkstra.delete@this.ntlworld.com), May 15, 2013 5:37 pm
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).
Which Linux benchmarks do you mean? This does not show a single benchmark where dual Atom can keep up with dual A15. Even Tegra 3 wins 9 out of 11 benchmarks despite its slow single-channel memory system.
> 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.
"Intel is claiming" - there is your hint... When Atom originally was announced, it was supposed to be 5-6 times faster than ARM cores. However when Atom was finally available in phones, it actually lagged in performance. This is where Atom is today. Is that competitive?
> A couple of questions then:
>
> 1. How can a narrower design pull this off?
It doesn't. Not without trickery anyway - like comparing a highly clocked CPU against a low clocked one, comparing an unreleased CPU against a much older CPU, using different compiler versions or optimizing for specific benchmarks (SunSpider). It's called "benchmarketing"...
> 2. Is this likely to be integer only as A15 includes FMAC instructions,
> which in the right cases double FPU performance?
ARM also has MAC on the integer side. Although both effectively double the theoretical max MOPS/FLOPS on a few kernels, you wouldn't expect twice performance on typical code.
About the only area where Silvermont appears to have an advantage over A15 is a lower L2 latency. Everything else is like you said, smaller buffers, narrower, simpler and less aggressive. Given the memory system advantage I'd expect it to beat A9 by a good margin (although A9R4 might well be competitive). However based on what we know you'd have to be extremely optimistic to believe it can get even close to A15 performance.
Wilco
> 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).
Which Linux benchmarks do you mean? This does not show a single benchmark where dual Atom can keep up with dual A15. Even Tegra 3 wins 9 out of 11 benchmarks despite its slow single-channel memory system.
> 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.
"Intel is claiming" - there is your hint... When Atom originally was announced, it was supposed to be 5-6 times faster than ARM cores. However when Atom was finally available in phones, it actually lagged in performance. This is where Atom is today. Is that competitive?
> A couple of questions then:
>
> 1. How can a narrower design pull this off?
It doesn't. Not without trickery anyway - like comparing a highly clocked CPU against a low clocked one, comparing an unreleased CPU against a much older CPU, using different compiler versions or optimizing for specific benchmarks (SunSpider). It's called "benchmarketing"...
> 2. Is this likely to be integer only as A15 includes FMAC instructions,
> which in the right cases double FPU performance?
ARM also has MAC on the integer side. Although both effectively double the theoretical max MOPS/FLOPS on a few kernels, you wouldn't expect twice performance on typical code.
About the only area where Silvermont appears to have an advantage over A15 is a lower L2 latency. Everything else is like you said, smaller buffers, narrower, simpler and less aggressive. Given the memory system advantage I'd expect it to beat A9 by a good margin (although A9R4 might well be competitive). However based on what we know you'd have to be extremely optimistic to believe it can get even close to A15 performance.
Wilco
