Security Updates, Improved Instruction Performance and AVX-512 Updates

With every new microarchitecture update, there are goals on several fronts: add new instructions, decrease the latency of current instructions, increase the throughput of current instructions, and remove bugs. The big headline addition for Sunny Cove and Ice Lake is AVX-512, which hasn’t yet appeared on a mainstream widely distributed consumer processor – technically we saw it in Cannon Lake, but that was a limited run CPU. Nonetheless, a lot of what went into Cannon Lake also shows up in the Sunny Cove design. To complicate matters, AVX-512 comes in plenty of different flavors. But on top of that, Intel also made a significant number of improvements to a number of instructions throughout the design.

Big thanks to InstLatX64 for his help in analyzing the benchmark results.

Security

On security, almost all the documented hardware security fixes are in place with Sunny Cove. Through the CPUID results, we can determine that SSBD is enabled, as is IA32_ARCH_CAPABILITIES, L1D_FLUSH, STIBP, IBPB/IBRS and MD_CLEAR.

This aligns with Intel’s list of Sunny Cove security improvements:

Sunny Cove Security
AnandTech Description Name Solution
BCB Bound Check Bypass Spectre V1 Software
BTI Branch Target Injection Spectre V2 Hardware+OS
RDCL Rogue Data Cache Load V3 Hardware
RSSR Rogue System Register Read V3a Hardware
SSB Speculative Store Bypass V4 Hardware+OS
L1TF Level 1 Terminal Fault Foreshadow Hardware
MFBDS uArch Fill Buffer Data Sampling RIDL Hardware
MSBDS uArch Store Buffer Data Sampling Fallout Hardware
MLPDS uArch Load Port Data Sampling - Hardware
MDSUM uArch Data Sampling Uncachable Memory - Hardware

Aside from Spectre V1, which has no suitable hardware solution, almost all of the rest have been solved through hardware/firmware (Intel won’t distinguish which, but to a certain extent it doesn’t matter for new hardware). This is a step in the right direction, but of course it may have a knock-on effect, plus for anything that gets performance improvements being moved from firmware to hardware will be rolled into any advertised IPC increase.

Also on the security side is SGX, or Intel’s Software Guard Instructions. Sunny Cove now becomes Intel’s first public processor to enable both AVX-512 and SGX in the same design. Technically the first chip with both SGX and AVX-512 should have been Skylake-X, however that feature was ultimately disabled due to failing some test validation cases. But it now comes together for Sunny Cove in Ice Lake-U, which is also a consumer processor.

Instruction Improvements and AVX-512

As mentioned, Sunny Cove pulls a number of key improvements from the Cannon Lake design, despite the Cannon Lake chip having the same cache configuration as Skylake. One of the key points here is the 64-bit division throughput, which goes from a 97-cycle latency to an 18-cycle latency, blowing past AMD’s 45-cycle latency. As an ex-researcher with no idea about instruction latency or compiler options, working on high-precision math code, this speedup would have been critical.

  • IDIV -> 97-cycle to 18-cycle

For the general purpose registers, we see a lot of changes, and most of them quite sizable.

Sunny Cove GPR Changes
AnandTech Instruction Skylake Sunny Cove
Complex LEA Complex Load Effective Address 3 cycle latency
1 per cycle
1 cycle latency
2 per cycle
SHL/SHR Shift Left/Right 2 cycle latency
0.5 per cycle
1 cycle latency
1 per cycle
ROL/ROR Rotate Left/Right 2 cycle latency
0.5 per cycle
1 cycle latency
1 per cycle
SHLD/SHRD Double Precision Shift Left/Right 4 cycle latency
0.5 per cycle
4 cycle latency
1 per cycle
4*MOV Four repated string MOVS Limited instructions 104 bits/clock
All MOVS* Instructions

In the past we’ve seen x87 instructions being regressed, made slower, as they become obsolete. For whatever reason, Sunny Cove decreases the FMUL latency from 5 cycles to 4 cycles.

The SIMD units also go through some changes:

Sunny Cove SIMD
AnandTech Instruction Skylake Sunny Cove
SIMD Packing SIMD Packing now slower 1 cycle latency
1 per cycle
3 cycle latency
1 per cycle
AES* AES Crypto Instructions
(for 128-bit / 256-bit)
4 cycle latency
2 per cycle
3 cycle latency
2 per cycle
CLMUL Carry-Less Multiplication 7 cycle latency
1 per cycle
6 cycle latency
1 per cycle
PHADD/PHSUB Packed Horizontal Add/Subtract
and Saturate
3 cycle latency
0.5 per cycle
2 cycle latency
1 per cycle
VPMOV* xmm Vector Packed Move 2 cycle latency
0.5 per cycle
2 cycle latency
1 per cycle
VPMOV* ymm Vector Packed Move 4 cycle latency
0.5 per cycle
2 cycle latency
1 per cycle
VPMOVZX/SX* xmm Vector Packed Move 1 cycle latency
1 per cycle
1 cycle latency
2 per cycle
POPCNT Microcode 50% faster than SW (under L1-D size)
REP STOS* Repeated Store String 62 bits/cycle 54 bits/cycle
VPCONFLICT Still Microcode Only

We’ve already gone through all of the new AVX-512 instructions in our Sunny Cove microarchitecture disclosure. These include the following families:

  • AVX-512_VNNI (Vector Neural Network Instructions)
  • AVX-512_VBMI (Vector Byte Manipulation Instructions)
  • AVX-512_VBMI2 (second level VBMI)
  • AVX-512_ BITALG (bit algorithms)
  • AVX-512_IFMA (Integer Fused Multiply Add)
  • AVX-512_VAES (Vector AES)
  • AVX-512_VPCLMULQDQ (Carry-Less Multiplacation of Long Quad Words)
  • AVX-512+GFNI (Galois Field New Instructions)
  • SHA (not AVX-512, but still new)
  • GNA (Gaussian Neural Accelerator)

(Intel also has the GMM (Gaussian Mixture Model) inside the core since Skylake, but I’ve yet to see any information on this outside a single line in the coding manual.)

For all these new AVX-512 instructions, it’s worth noting that they can be run in 128-bit, 256-bit, or 512-bit mode, depending on the data types passed to it. Each of these can have corresponding latencies and throughputs, which often get worse when going for the 512-bit mode, but overall assuming you can fill the register with a 512-bit data type, then the overall raw processing will be faster, even with the frequency differential. This doesn’t take into account any additional overhead for entering the 512-bit power state, it should be noted.

Most of these new instructions are relatively fast, with most of them only 1-3 cycles of latency. We observed the following:

Sunny Cove Vector Instructions
AnandTech Instruction XMM YMM ZMM
VNNI Latency Vector Neural Network Instructions 5-cycle 5-cycle 5-cycle
Throughput 2/cycle 2/cycle 1/cycle
VPOPCNT* Latency Return the number of bits set to 1 3-cycle 3-cycle 3-cycle
Throughput 1/cycle 1/cycle 1/cycle
VPCOMPRESS* Latency Store Packed Data 3-cycle 3-cycle 3-cycle
Throughput 0.5/cycle 0.5/cycle 0.5/cycle
VPEXPAND* Latency Load Packed Data 5-cycle 5-cycle 5-cycle
Throughput 0.5/cycle 0.5/cycle 0.5/cycle
VPSHLD* Latency Vector Shift 1-cycle 1-cycle 1-cycle
Throughput 2/cycle 2/cycle 1/cycle
VAES* Latency Vector AES Instructions 3-cycle 3-cycle 3-cycle
Throughput 2/cycle 2/cycle 1/cycle
VPCLMUL Latency Vector Carry-Less Multiply 6-cycle 8-cycle 8-cycle
Throughput 1/cycle 0.5/cycle 0.5/cycle
GFNI Latency Galois Field New Instructions 3-cycle 3-cycle 3-cycle
Throughput 2/cycle 2/cycle 1/cycle

For all of the common AVX2 instructions, xmm/ymm latencies and throughputs are identical to Skylake, however zmm is often a few cycles slower for DIV/SQRT variants.

Other Noticeable Observations

From our testing, we were also able to prove some of the other parts of the core, such as the added store ports and shuffle units.

Our data shows that the second store port is not identical to the first, which explains the imbalance when it comes to writes: rather than supporting 2x64-bit with loads, it only supports either 1x64-bit write, or 1x32-bit write, or 2x16-bit writes. This means we mainly see speed ups with GPR/XMM data, and the result is only a small improvement for 512-bit SCATTER instructions. Otherwise, it seems not to work with any 256-bit or 512-bit operand (you can however use it with 64-bit AVX-512 mask registers). This is going to cause a slight headache for anyone currently limited by SCATTER stores.

The new shuffle unit is only 256-bit wide. It will handle a number of integer instructions (UNPCK, PSLLDQ, SHUF*, MOVSHDUP, but not PALIGNR or PACK), but only a couple of floating point instructions (SHUFPD, SHUFPS).

Cache and TLB Updates SPEC2017 and SPEC2006 Results (15W)
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  • tamalero - Monday, August 5, 2019 - link

    the 3d mark VRS test graph is very confusing. Reply
  • MASSAMKULABOX - Tuesday, August 6, 2019 - link

    These chips are priced quite high esp the i3's the Dualcore is outrageous (20$ discount for half the cores and threads?).They will only sell in limited qtys at such high prices . Bring on the 14nm equiv at sane prices.
    what discrete gfx does the IGPU equate to? gt1030 vs 2200g vs 3400ge??
    Reply
  • Zhentar - Tuesday, August 6, 2019 - link

    The bit per cycle throughput of REP STOS is really only half of the picture - the startup latency matters a lot too! On my Skylake, I've measured a minimum latency of 29 cycles* (any REP STOS from 1 byte to 128 bytes takes 29 cycle, then it starts going up from there). Some compilers make heavy use of it even for small stores/copies (VC6, first and foremost, but also the .NET JIT for stack zeroing), so it can be pretty important to performance in some scenarios.

    *I am no Agner Fog... nor anywhere close to him, this measurement should be taken with a grain of salt ;-)
    Reply
  • ballsystemlord - Wednesday, August 7, 2019 - link


    @Ian
    Sunny Cove SIMD chart and others have many asterisks, why?

    "POPCNT Microcode 50% faster than SW (under L1-D size)"
    What does this mean? The CPU uses microcode and HW, not SW, AFAIK, much less use it to implement the POPCNT instruction.
    Reply
  • ballsystemlord - Thursday, August 8, 2019 - link

    Spelling and grammar errors:
    Insert: I've been commenting corrections for at least 1 year now, if you guys want me to change the format, or have any request regarding phrasing, etc., just ask. Thanks for your work!

    "L3 latencies look similar, however we'll dwell into that just in a bit."
    I think you ment delve:
    "L3 latencies look similar, however we'll delve into that just in a bit."

    "IPC increases against the mobile Skylake are 33 and 38% in the integer and fp suites, though we also have to keep in d mind these figures go beyond just the Sunny Cove architecture and also include improvements through the new LPDDR4X memory controllers."
    Missing percent sign and stray "d".
    "IPC increases against the mobile Skylake are 33% and 38% in the integer and fp suites, though we also have to keep in mind these figures go beyond just the Sunny Cove architecture and also include improvements through the new LPDDR4X memory controllers."

    "...which did not go down to well."
    You mean "too" not "to":
    "...which did not go down too well."

    "...we actually see a number of key microarchitectural improvements bubble up through in our SPEC testing."
    Excess "in":
    "...we actually see a number of key microarchitectural improvements bubble up through our SPEC testing."
    Reply
  • alysdexia - Thursday, November 28, 2019 - link

    I think you mean Baalsystemlord or Bàqhàlsýstemlord.
    Grammar is a barbarism of ghrammatics, another word for composition or handwriting, font, format, spacing, the looks, whereas you meant diction/lecsis or register, vocabulary, declension, placement, spelling, the meaning.
    you guys -> ye
    Reply
  • nils_ - Monday, August 19, 2019 - link

    I noticed on Intel Ark that Ice Lake CPUs do not have TSX instructions enabled / available. THis is interesting, since I believe TSX has also been used for some of the spectre attacks. Reply
  • ikjadoon - Thursday, September 12, 2019 - link

    On 'Gaming Results (15W and 25W)', the graph is colored incorrectly. "On" and "Off" have the same color...and the legend colors are somehow not related to the graphic? Reply

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