CPU Performance: Meet Kryo

To dive right into the heart of matters then, after getting our standard benchmarks out of the way we had enough time left to load up some of our more advanced analysis tools to run on the 820 MDP/S. While Qualcomm has been somewhat forthcoming in the Kryo CPU architecture, they have never been as forward as say ARM (who is in the business of licensing the IP), so there are still some unanswered questions about what Kryo is like under the hood.

Qualcomm CPU Core Comparison
  Snapdragon 800 Snapdragon 810 Snapdragon 820
CPU Codename Krait ARM Cortex-A57 Kryo
ARM ISA ARMv7-A (32-bit) ARMv8-A (32/64-bit) ARMv8-A (32/64-bit)
Integer Add 1 2 1
Integer Mul 1 1 1
Shifter ALUs 1 2 1
Addition (FP32) Latency 3 cycles 5 cycles 3 cycles
Multiplication (FP32) Latency 6 cycles 5 cycles 5 cycles
Addition (INT) Latency 1.5 cycles 1 cycle 1 cycle
Multiplication (INT) Latency 4 cycles 3 cycles 4 cycles
L1 Cache 16KB I$ + 16KB D$ 48KB I$ + 32KB D$ 32KB I$ + 32KB D$?
L3 Cache N/A N/A N/A

One thing that immediately jumps out is how similar some of our results are to Krait. According to our initial tests, the number of integer and FP ALUs would appear to be unchanged. Similarly the latency for a lot of operations is similar as well. This isn’t wholly surprising as Krait was a solid architecture for Qualcomm, and there is a good chance they agreed and decided to use it as their starting point. At the same time however I do want to note that these are our initial results done rather quickly on what’s essentially a beta device; further poking later on may reveal more differences than what we’ve seen so far.

But with the above said, there’s a big difference between how many execution units a CPU design has and how well it can fill them, which is why even similar designs can have wildly different IPC. We’ll investigate this a bit more in a moment, however it’s worth noting that this is exactly the philosophy ARM has gone into with Cortex-A72, so it is neither unprecedented nor even unexpected.

Looking at the memory hierarchy and latency, our results point to a 32KB L1 data cache. For the moment I’m assuming the instruction cache is identical, as is the case on most designs, but this test is purely a data test. Meanwhile L2 cache size is a bit harder to pin down; we know that the different CPU clusters on 820 will be using different L2 cache sizes. Ultimately it's pretty much impossible to pin down the exact L2 cache size from this test alone, especially since we can't see the amount of L2 attached to the lower clocked Kryo cluster.

According to our colleague Matt Humrick over at Tom's Hardware, while investigating the matter, it seems that Qualcomm disclosed that we're looking at an 1MB L2 for the performance cluster and a 512KB L2 for the power cluster. We're still looking into independently confirming this bit of information with Qualcomm.

However what you won’t find – and much to our surprise – is an L3 cache. Our test results indicate (and Qualcomm confirms) that Snapdragon 820 does not have an L3 cache as we initially expected, with the L2 cache being the highest cache level on the chip. We initially reported there to be an L3 due to the fact that we found evidence and references to this cache block in Qualcomm's resources, but it seems the latest revision of the SoC doesn't actually employ such a piece in actual silicon, as demonstrated by the latency graph. This means that there isn’t any kind of cache back-stopping interactions between the two CPU clusters, or between the CPU and GPU. Only simple coherency, and then beyond that main memory.

Geekbench 3 Memory Bandwidth Comparison (1 thread)
  Stream Copy Stream Scale Stream Add Stream Triad
SD 801 (2458MHz) 7.6 GB/s 4.6 GB/s 4.6 GB/s 5.2 GB/s
SD 810 (1958MHz) 7.5 GB/s 7.4 GB/s 6.4 GB/s 6.6GB/s
SD 820 (2150MHz) 17.4 GB/s 11.5 GB/s 13.1 GB/s 12.8 GB/s
SD 820 > 810 Advantage 131% 55% 103% 94%

Meanwhile looking at Geekbench 3 memory performance, one can see that memory bandwidth is greatly improved over both Snapdragon 800/801 and 810. Stream copy in particular is through the roof, increasing by 131% (over double 810’s performance). Even the other tests, though not as great, are between 55% and 103%. The Snapdragon 820 also shows improved latency to main memory when compared to the Snapdragon 810, so it seems that Qualcomm made definite improvements in the memory controller and general memory architecture of the chipset, allowing the CPUs to get nearer to the theoretical total memory bandwidth offered by the memory controllers.

Moving on, let’s shift to some benchmarks that make a more comprehensive look at performance, starting with SPECint2000. Developed by the Standard Performance Evaluation Corporation, SPECint2000 is the integer component of their larger SPEC CPU2000 benchmark. Designed around the turn of the century, officially SPEC CPU2000 has been retired for PC processors, but with mobile processors roughly a decade behind their PC counterparts in performance, SPEC CPU2000 is currently a very good fit for the capabilities contemporary SoCs.

SPECint2000 - Estimated Scores
  Snapdragon 810 Snapdragon 820 % Advantage
164.gzip
823
1176
43%
175.vpr
2456
1707
-30%
176.gcc
1341
1641
22%
181.mcf
789
593
-25%
186.crafty
1492
1449
-3%
197.parser
753
962
28%
252.eon
2321
3333
44%
253.perlbmk
1090
1384
27%
254.gap
1325
1447
9%
255.vortex
1043
1583
52%
256.bzip2
867
1041
20%
300.twolf
DNC
DNC
N/A

Even though this early preview means we don’t have the luxury of building a binary with a compiler aware of Kryo, using our A57 binaries produces some preliminary results on the 820 MDP/S. Performance does regress in a couple of places – but in other places we see performance increases by up to 52%. 820 does have a slight 10% frequency advantage over 810, so when taking into account the clock difference the IPC improvements are slightly lower. This is also showcased when comparing the Snapdragon 820 to a more similarly clocked Exynos 7420 (A57 @ 2100MHz), where the maximum advantage drops to 33% and similarly to a clock-normalized Snapdragon 810, the overall average comes in at only 5-6%. Once we get the opportunity to have more time with a Snapdragon 820 device we'll be able to verify how much the compiler settings affect the score on the Kryo architecture.

Our other set of comparison benchmarks comes from Geekbench 3. Unlike SPECint2000, Geekbench 3 is a mix of integer and floating point workloads, so it will give us a second set of eyes on the integer results along with a take on floating point improvements.

Geekbench 3 - Integer Performance
  Snapdragon 810 Snapdragon 820 % Advantage
AES ST
739.7 MB/s
700.7 MB/s
-5%
AES MT
3.05 GB/s
1.99 GB/s
-35%
Twofish ST
89.8 MB/s
102.7 MB/s
14%
Twofish MT
448.5 MB/s
345.5 MB/s
-23%
SHA1 ST
628.9 MB/s
983 MB/s
56%
SHA1 MT
3.02 GB/s
2.84 GB/s
-6%
SHA2 ST
83.5 MB/s
134.9 MB/s
61%
SHA2 MT
393.4 MB/s
374.6 MB/
-5%
BZip2Comp ST
5.01 MB/s
7.29 MB/s
45%
BZip2Comp MT
20.5 MB/s
20.5 MB/s
0%
Bzip2Decomp ST
7.99 MB/s
9.76 MB/s
24%
Bzip2Decomp MT
30.8 MB/s
24.9 MB/s
-19%
JPG Comp ST
18.9 MP/s
23.3 MP/s
23%
JPG Comp MT
88.9 MP/s
76.7 MP/s
-14%
JPG Decomp ST
41.5 MP/s
62.2 MP/s
49%
JPG Decomp MT
182.7 MP/s
176.6 MP/s
-3%
PNG Comp ST
1.11 MP/s
1.56 MP/s
43%
PNG Comp MT
4.78 MP/s
4.61 MP/s
-4%
PNG Decomp ST
17.9 MP/s
24.2 MP/s
35%
PNG Decomp MT
94.1 MP/s
64.3 MPs
-32%
Sobel ST
53.3 MP/s
86.3 MP/s
62%
Sobel MT
248.4 MP/s
244.8 MP/s
-1%
Lua ST
1.30 MB/s
1.59 MB/s
22%
Lua MT
5.93 MB/s
4.5 MB/s
-24%
Dijkstra ST
3.38 Mpairs/s
5.52 Mpairs/s
63%
Dijkstra MT
13.7 Mpairs/s
13.7 Mpairs/s
0%

The actual integer performance gains with GeekBench 3 are rather varied. Single-threaded results consistently show gains, ranging from a minor -5% regression for AES up to a 61% improvement for SHA2. Given the architecture shift involved here, this is a bit surprising (and in Qualcomm’s favor) since you wouldn’t necessarily expect Kryo to beat Cortex-A57 on everything. On the other hand MT results typically show a regression, since Snapdragon 810 had a 4+4 big.LITTLE configuration that meant that it had the 4 Cortex-A53 cores contributing to the task, along with the big cores all running at their near-full clockspeed, while Kryo’s second cluster runs at a reduced clockrate. And though one could have a spirited argument about whether single-threaded or multi-threaded performance is more important, I’m firmly on the side of ST for most use cases.

Geekbench 3 - Floating Point Performance
  Snapdragon 810 Snapdragon 820 % Advantage
BlackScholes ST
5.46 Mnodes/s
12.3 Mnodes/s
125%
BlackScholes MT
25.5 Mnodes/s
32.1 Mnodes/s
26%
Mandelbrot ST
1.2 GFLOPS
2 GFLOPS
67%
Mandelbrot MT
6.41 GFLOPS
6.23 GFLOPS
-3%
Sharpen Filter ST
1.07 GFLOPS
2.15 GFLOPS
100%
Sharpen Filter MT
5.02 GFLOPS
6.11 GFLOPS
22%
Blur Filter ST
1.27 GFLOPS
3.14 GFLOPS
147%
Blur Filter MT
6.14 GFLOPS
8.84 GFLOPS
44%
SGEMM ST
2.29 GFLOPS
4.09 GFLOPS
79%
SGEMM MT
6.12 GFLOPS
9.19 GFLOPS
50%
DGEMM ST
1.05 GFLOPS
1.95 GFLOPS
85%
DGEMM MT
2.81 GFLOPS
4.53 GFLOPS
61%
SFFT ST
1.25 GFLOPS
1.98 GFLOPS
58%
SFFT MT
4.11 GFLOPS
5.65 GFLOPS
37%
DFFT ST
1.03 GFLOPS
1.68 GFLOPS
63%
DFFT MT
2.97 GFLOPS
4.76 GFLOPS
60%
N-Body ST
486.6 Kpairs/s
841 Kpairs/s
73%
N-Body MT
1.72 Mpairs/s
2.34 Mpairs/s
36%
Ray Trace ST
1.84MP/s
2.86 MP/s
55%
Ray Trace MT
8.16 MP/s
8.46 MP/s
4%

GeekBench 3’s floating point results are even more positive for Snapdragon 820. There is only a single performance regression, a -3% in Mandelbrot multi-threaded. Otherwise in both MT and ST workloads, performance is significantly up. This is a prime example of where Kryo is taking better advantage of its execution units than any high-end Qualcomm SoC before it, as even holding steady (or on paper having a slight deficit) it in practice comes out significantly ahead.

The Qualcomm Snapdragon 820 Performance Preview CPU Performance, Cont
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  • kspirit - Thursday, December 10, 2015 - link

    What are the chances this shows up in the Galaxy S7? Because let's be honest, a large reason of Qualcomm's drop in revenue is because Samsung is sticking to their own chips now. But the 820 looks interesting indeed. Reply
  • Clayevans - Thursday, December 10, 2015 - link

    Probably better than the chance that this will show up in the iPhone 7, haha. But in all seriousness, I think everyone would be very surprised to see Sammy switch back. Any specific guesses on my part would be pure BS. Reply
  • close - Friday, December 11, 2015 - link

    It will probably use multiple sourcing like other models do. So Samsung may sell enough phones to have the need to also source SoCs from Qualcomm. Also Samsung sells their Exynos SoC to other vendors so the entire production is not dedicated for internal use. Reply
  • frostyfiredude - Sunday, December 13, 2015 - link

    There are a lot of complaints of network issues because of the S6's Shannon modem, in NA especially on both the operator and client sides; a return to the previous method of doing US/Canada with Qualcomm and everyone else Exynos seems likely for that reason. Especially since S820 seems quite decent. Reply
  • jjj - Thursday, December 10, 2015 - link

    The rumors were that Qualcomm gets the CDMA carriers while everything else,including international unlocked version, is Exynos.
    Samsung would save a lot of money with their own SoC so they would use something else only if there was a very good reason to. The perf here doesn't seem like a good enough reason.
    Reply
  • Clayevans - Thursday, December 10, 2015 - link

    I remember back in the early days of Exynos, the USA galaxy phones would get snapdragon simply because Sammy couldn't produce enough of their own to cover global demand. They don't have that problem anymore. And like you said, there really aren't any compelling reasons for them to go back to Snapdragon that would justify the cost. Reply
  • jjj - Thursday, December 10, 2015 - link

    In fairness the CPU perf is great, sure it doesn't seem like it will crush A72 but compared to SD801 the perf is fantastic - SD810 was terrible so can be ignored.
    In Geekbench in integer and FP it's over 2x the SD801 in single core and that's insane in a phone.That's why a comparison with older desktop cores would be nice. CPU perf is clearly hitting good enough in phones.
    The memory perf is stupid good here.
    2016 is exciting, what SoC wins doesn't really matter, we the users certainly win.
    Reply
  • mmrezaie - Thursday, December 10, 2015 - link

    How can you say performance is great?! It is actually at best as good as A72 performances reported so far, and not even on a same node size. So what was all the reason behind research and development when you build something as good as ARM's offering. No wonder other companies feel safe using ARM for their SOCs. I don't think samsung will go for this if they can manufacture their SOC in time. Reply
  • ddriver - Thursday, December 10, 2015 - link

    Judging from the name, it will take Kryogenic cooling to really shine ;) Reply
  • BurntMyBacon - Monday, December 14, 2015 - link

    @ddriver: "Judging from the name, it will take Kryogenic cooling to really shine ;)"

    Oh. I thought it meant that kryotic was used in the manufacturing process. ;')
    Thanks for clearing that up.
    Reply

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