How does Krait compare to Cortex-A7?

[pantsaregood]

Per-clock, how do these cores compare? I've noticed quad-core Cortex-A7s showing up in low/medium range phones a lot more recently, but I've not really seen a direct comparison of per-core per-clock performance of the cores.

 

[s44]

You mean the Krait 400/450 that's in the Snapdragon 800/801/805?

That's in the same ballpark as the A15 - actually a bit slower, but clocks higher.

The A7 is about equivalent to the A8, which is the one we saw in the iPhone 4, original Galaxy S, etc - the tail end of the single-core era (all the dual core since has been A9 or newer).

I believe that in actual use the quad A7 ended up in the same ballpark as the dual Krait 300 that was the other Snapdragon 400 configuration. Slower in single-threaded but similar in multithreaded and more power-efficient.

Check out the roadmap from a year ago here:
http://www.anandtech.com/show/7126/the-arm-diaries-part-2-understanding-the-cortex-a12
(though of course fab process progress has been really disappointing)

 

[pantsaregood]

Well, the Krait 400 is a quad-core configuration. I'm just interested in a knowing how a single Krait core compares to a single A7 core at the same clock speed.

I suppose I'm interested in Krait 300/4xx, though.

 

[Trombe]

Approximately 75% better in favor of Krait if you go by DMIPS/theory. Real world will of course vary.

 

[s44]

Well, the Krait 400 is a quad-core configuration.

No it's not. Krait is the core name. Snapdragon is the SOC name.

*Snapdragon* 400 (current budget version) uses 4 A7 cores.
*Snapdragon* 400 (original version - 2012 flagships) used 2 Krait 300 cores.
*Snapdragon* 600 (2013 flagships) used 4 Krait 300 cores.
*Snapdragon* 800 uses 4 Krait 400 cores.

Etc.

 

[pantsaregood]

Is there any difference between Krait 300 and Krait 400 other than the clockspeeds the cores are rated for? I'm aware that Krait is the name of the core (just as Scorpion was previously), but I was under the impression that Krait 400 was just a quad-core Krait configuration.

 

[s44]

Is there any difference between Krait 300 and Krait 400 other than the clockspeeds the cores are rated for? I'm aware that Krait is the name of the core (just as Scorpion was previously), but I was under the impression that Krait 400 was just a quad-core Krait configuration.

No. There already *was* a quad Krait (300) in the Snapdragon 600 (Galaxy S4, original One, etc.). Krait 400 was the next iteration.

As for the actual differences, Brian said:

Krait 400 improves L2 access latencies over Krait 300 (which is at the heart of Snapdragon 600 and S4 Pro) and is optimized for higher frequency operation, but Krait 400 is otherwise architecturally similar to Krait 300.

 

[Rdmkr]

I believe that in actual use the quad A7 ended up in the same ballpark as the dual Krait 300 that was the other Snapdragon 400 configuration. Slower in single-threaded but similar in multithreaded and more power-efficient.

The higher the priority (in terms of impact on user-experience) of the task, the more important the single-threaded performance is. On that note I do think the quad A7 is significantly slower in practice than even that ancient chip, especially accounting for the fact that the A7s are typically clocked at 1.2Ghz instead of the Krait 400 MK1's 1.5Ghz.

ps. if there is some award for confusing naming schemes, qualcomm should get it.

 

[pantsaregood]

So, Nokia recently released the Lumia 530. It has a quad-core Cortex-A7 at 1.2 GHz and an Adreno 302. It is intended to replace the Lumia 520, which ran a dual-core 1.0 GHz Krait and Adreno 305. Both devices run 512 MB of RAM.

Is this even an upgrade? Benchmarks say the 530 is significantly faster, but I don't understand how unless it is driver related.

http://www.wpcentral.com/lumia-520-versus-lumia-530-benchmarks

 

[Rdmkr]

A few remarks:
- energy efficiency wise the new snapdragon 400 will do very well. This also means it eats less into the heating-budget of whatever device its in, meaning it gets throttled less

- an SoC is composed of more than just cores, clock speed and microachitecture; if the rest forms a bottleneck to the Krait chip it underperforms compared to its potential

- qualcomm is notorious for using confusing names for its chips; not unlikely that 302 GPU is a faster variant despite the lower model number. And again, more power efficiency can mean less throttling, so the theoretically "weaker" chip can sometimes win.

- 1.0Ghz is a very, very low clock speed. in situations where the broad pipeline of the Krait chip can't be utilized, it will do as poorly as any other dual-core CPU clocked that low

- benchmarks do tend to overstate the impact of an increased core count, so some of the numbers you see should be taken with a grain of salt.

On the whole you can probably trust those benchmarks numbers more than you can trust compositional analyses of the CPU's parts, though; there are a lot of saving clauses to forming these analyses and ultimately it's more of an art than a science.