As part of today’s International Supercomputing 2021 (ISC) announcements, Intel is showcasing that it will be launching a version of its upcoming Sapphire Rapids (SPR) Xeon Scalable processor with high-bandwidth memory (HBM). This version of SPR-HBM will come later in 2022, after the main launch of Sapphire Rapids, and Intel has stated that it will be part of its general availability offering to all, rather than a vendor-specific implementation.

Hitting a Memory Bandwidth Limit

As core counts have increased in the server processor space, the designers of these processors have to ensure that there is enough data for the cores to enable peak performance. This means developing large fast caches per core so enough data is close by at high speed, there are high bandwidth interconnects inside the processor to shuttle data around, and there is enough main memory bandwidth from data stores located off the processor.


Our Ice Lake Xeon Review system with 32 DDR4-3200 Slots

Here at AnandTech, we have been asking processor vendors about this last point, about main memory, for a while. There is only so much bandwidth that can be achieved by continually adding DDR4 (and soon to be DDR5) memory channels. Current eight-channel DDR4-3200 memory designs, for example, have a theoretical maximum of 204.8 gigabytes per second, which pales in comparison to GPUs which quote 1000 gigabytes per second or more. GPUs are able to achieve higher bandwidths because they use GDDR, soldered onto the board, which allows for tighter tolerances at the expense of a modular design. Very few main processors for servers have ever had main memory be integrated at such a level.


Intel Xeon Phi 'KNL' with 8 MCDRAM Pads in 2015

One of the processors that used to be built with integrated memory was Intel’s Xeon Phi, a product discontinued a couple of years ago. The basis of the Xeon Phi design was lots of vector compute, controlled by up to 72 basic cores, but paired with 8-16 GB of on-board ‘MCDRAM’, connected via 4-8 on-board chiplets in the package. This allowed for 400 gigabytes per second of cache or addressable memory, paired with 384 GB of main memory at 102 gigabytes per second. However, since Xeon Phi was discontinued, no main server processor (at least for x86) announced to the public has had this sort of configuration.

New Sapphire Rapids with High-Bandwidth Memory

Until next year, that is. Intel’s new Sapphire Rapids Xeon Scalable with High-Bandwidth Memory (SPR-HBM) will be coming to market. Rather than hide it away for use with one particular hyperscaler, Intel has stated to AnandTech that they are committed to making HBM-enabled Sapphire Rapids available to all enterprise customers and server vendors as well. These versions will come out after the main Sapphire Rapids launch, and entertain some interesting configurations. We understand that this means SPR-HBM will be available in a socketed configuration.

Intel states that SPR-HBM can be used with standard DDR5, offering an additional tier in memory caching. The HBM can be addressed directly or left as an automatic cache we understand, which would be very similar to how Intel's Xeon Phi processors could access their high bandwidth memory.

Alternatively, SPR-HBM can work without any DDR5 at all. This reduces the physical footprint of the processor, allowing for a denser design in compute-dense servers that do not rely much on memory capacity (these customers were already asking for quad-channel design optimizations anyway).

The amount of memory was not disclosed, nor the bandwidth or the technology. At the very least, we expect the equivalent of up to 8-Hi stacks of HBM2e, up to 16GB each, with 1-4 stacks onboard leading to 64 GB of HBM. At a theoretical top speed of 460 GB/s per stack, this would mean 1840 GB/s of bandwidth, although we can imagine something more akin to 1 TB/s for yield and power which would still give a sizeable uplift. Depending on demand, Intel may fill out different versions of the memory into different processor options.

One of the key elements to consider here is that on-package memory will have an associated power cost within the package. So for every watt that the HBM requires inside the package, that is one less watt for computational performance on the CPU cores. That being said, server processors often do not push the boundaries on peak frequencies, instead opting for a more efficient power/frequency point and scaling the cores. However HBM in this regard is a tradeoff - if HBM were to take 10-20W per stack, four stacks would easily eat into the power budget for the processor (and that power budget has to be managed with additional controllers and power delivery, adding complexity and cost).

One thing that was confusing about Intel’s presentation, and I asked about this but my question was ignored during the virtual briefing, is that Intel keeps putting out different package images of Sapphire Rapids. In the briefing deck for this announcement, there was already two variants. The one above (which actually looks like an elongated Xe-HP package that someone put a logo on) and this one (which is more square and has different notches):

There have been some unconfirmed leaks online showcasing SPR in a third different package, making it all confusing.

 

Sapphire Rapids: What We Know

Intel has been teasing Sapphire Rapids for almost two years as the successor to its Ice Lake Xeon Scalable family of processors. Built on 10nm Enhanced SuperFin, SPR will be Intel’s first processors to use DDR5 memory, have PCIe 5 connectivity, and support CXL 1.1 for next-generation connections. Also on memory, Intel has stated that Sapphire Rapids will support Crow Pass, the next generation of Intel Optane memory.

For core technology, Intel (re)confirmed that Sapphire Rapids will be using Golden Cove cores as part of its design. Golden Cove will be central to Intel's Alder Lake consumer processor later this year, however Intel was quick to point out that Sapphire Rapids will offer a ‘server-optimized’ configuration of the core. Intel has done this in the past with both its Skylake Xeon and Ice Lake Xeon processors wherein the server variant often has a different L2/L3 cache structure than the consumer processors, as well as a different interconnect (ring vs mesh, mesh on servers).

Sapphire Rapids will be the core processor at the heart of the Aurora supercomputer at Argonne National Labs, where two SPR processors will be paired with six Intel Ponte Vecchio accelerators, which will also be new to the market. Today's announcement confirms that Aurora will be using the SPR-HBM version of Sapphire Rapids.

As part of this announcement today, Intel also stated that Ponte Vecchio will be widely available, in OAM and 4x dense form factors:

Sapphire Rapids will also be the first Intel processors to support Advanced Matrix Extensions (AMX), which we understand to help accelerate matrix heavy workflows such as machine learning alongside also having BFloat16 support. This will be paired with updates to Intel’s DL Boost software and OneAPI support. As Intel processors are still very popular for machine learning, especially training, Intel wants to capitalize on any future growth in this market with Sapphire Rapids. SPR will also be updated with Intel’s latest hardware based security.

It is highly anticipated that Sapphire Rapids will also be Intel’s first multi compute-die Xeon where the silicon is designed to be integrated (we’re not counting Cascade Lake-AP Hybrids), and there are unconfirmed leaks to suggest this is the case, however nothing that Intel has yet verified.

The Aurora supercomputer is expected to be delivered by the end of 2021, and is anticipated to not only be the first official deployment of Sapphire Rapids, but also SPR-HBM. We expect a full launch of the platform sometime in the first half of 2022, with general availability soon after. The exact launch of SPR-HBM beyond HPC workloads is unknown, however given those time frames, Q4 2022 seems fairly reasonable depending on how aggressive Intel wants to attack the launch in light of any competition from other x86 vendors or Arm vendors. Even with SPR-HBM being offered to everyone, Intel may decide to prioritize key HPC customers over general availability.

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  • wumpus - Thursday, July 1, 2021 - link

    Especially useful considering that the HBM certainly has cache tags and I'd never expect it with DDR5. If you could add cache tags to DDR5 than HBM+DDR5+Optane would be even better, but also expensive to make.

    Putting the tags in the DDR5 would be iffy, unless the CPU is designed to accept motherboards designed specifically for this (with at least twice the minimum DDR5 width) and reading both banks of DDR5, checking the tags and only sending the right cachlines. Maybe you'd use a slew cache or something (limited to 1-way), as the DDR5 "cache" would be absolutely enormous compared to any other cache.

    But from what I've seen from Intel, don't expect any way to add tags to DDR5. And don't really expect Optane "DDR5" to be compatible with DDR5 (your motherboard would probably not be able to set the timings for the latency anyway).
    Reply
  • wumpus - Thursday, July 1, 2021 - link

    edit: with Micron throwing in the towel, I suspect there are real issues in making the whole thing work that Intel simply isn't talking about. They have all the rights to make this stuff and simply aren't interested. Reply
  • mode_13h - Friday, July 2, 2021 - link

    > Putting the tags in the DDR5 would be iffy

    Yeah, so just use the DDR5 as RAM and then swap to the Optane memory. That essentially gives you a software version of caching.
    Reply
  • JayNor - Monday, June 28, 2021 - link

    It would make more sense if HBM accesses didn't have to plug up L3. Something like the cxl direct attached memory on GPUs seems to be the use case, so why not implement it the same way...? Reply
  • mode_13h - Monday, June 28, 2021 - link

    > It would make more sense if HBM accesses didn't have to plug up L3.

    What do you mean by that? Are you saying you want HBM accesses to bypass L3?
    Reply
  • JayNor - Wednesday, June 30, 2021 - link

    I mean act as direct attached memory for the cores as on cxl gpu slaves.

    https://www.youtube.com/watch?v=OK7_89zm2io
    Reply
  • James5mith - Monday, June 28, 2021 - link

    Why the shortening of Sapphire Rapids to SPR? Sapphire is one word. Shouldn't it be SR? Reply
  • erotomania - Monday, June 28, 2021 - link

    I odn't know if journalists are the progenitors of the naming scheme or not, but it seems to be an Intel thing. I don't remember if every CPU generation/iteration received a three letter abbreviator, but IVB and KBL come to mind. By your logic, which is completely sound in my opinion, those should have been IB and KL. Reply
  • eastcoast_pete - Monday, June 28, 2021 - link

    In the pharmaceutical industry, "SR" stands for "slow release"; maybe Intel was tired of being the butt of even more jokes; they have been quite slow to release anything really new for a while now. Reply
  • mode_13h - Monday, June 28, 2021 - link

    Yeah, maybe Intel needs a project to accelerate their production cycle named after a laxative? Reply

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