27 March 2017

IBM Power 9 CPU a Game Changer.

IBM Power 9 CPU

IBM is looking to take a bigger slice out of Intel’s lucrative server business with Power9, the company’s latest and greatest processor for the datacenter. Scheduled for initial release in 2017, the Power9 promises more cores and a hefty performance boost compared to its Power8 predecessor. The new chip was described at the Hot Chips event.

IBM Power9 CPU

The Power9 will end up in IBM’s own servers, and if the OpenPower gods are smiling, in servers built by other system vendors. Although none of these systems have been described in any detail, we already know that bushels of IBM Power9 chips will end up in Summit and Sierra, two 100-plus-petaflop supercomputers that the US Department of Energy will deploy in 2017-2018. In both cases, most of the FLOPS will be supplied by NVIDIA Volta GPUs, which will operate alongside IBM’s processors.

Power 9 Processor For The Cognitive Era

The Power9 will be offered in two flavors: one for single- or dual-socket servers for regular clusters, and the other for NUMA servers with four or more sockets, supporting much larger amounts of shared memory. IBM refers to the dual-socket version is as the scale-out (SO) design and the multi-socketed version as the scale-up (SU) design. They basically correspond to the Xeon E5 (EP) and Xeon E7 (EX) processor lines, although Intel is apparently going to unify those lines post-Broadwell.

The SU Power9 is aimed at mission-critical enterprise work and other application where large amounts of shared memory are desired. It has extra RAS features, buffered memory, and will tend to have fewer cores running at faster clock rates. As such, it carries on many of the traditions of the Power architecture through Power8. The SU Power9 is going to be released in 2018, well after the SO version hits the streets.

The SO Power9 is going after the Xeon dual-socket server market in a more straightforward manner. These chips will use direct attached memory (DDR4) with commodity DIMMs, instead of the buffered memory setup mentioned above. In general, this processor will adhere to commodity packaging so that Power9-based servers can utilize industry standard componentry. This is the platform destined for large cloud infrastructure and general enterprise computing, as well as HPC setups. It’s due for release sometime next year.

Distilling out the differences between the two varieties, here are the basics of the new Power9 (Power8 specs in parentheses for comparison):

  • 8 billion transistors (4.2 billion)
  • Up to 24 cores (Up to 12 cores)
  • Manufactured using 14nm FinFET (22nm SOI)
  • Supports PCIe Gen4 (PCIe Gen3)
  • 120 MB shared L3 cache (96 MB shared L3 cache)
  • 4-way and 8-way simultaneous multithreading (8-way simultaneous multithreading)
  • Memory bandwidth of 120 or 230 GB/sec (230 GB/sec)

From the looks of things, IBM spent most of the extra transistor budget it got from the 14nm shrink on extra cores and a little bit more L3 cache. New on-chip data links were also added, with an aggregate bandwidth of 7 TB/sec, which is used to feed each core at the rate of 256 GB/sec in a 12-core configuration. The bandwidth fans out in the other direction to supply data to memory, additional Power9 sockets, PCIe devices, and accelerators. Speaking of which, there is special support for NVIDIA GPUs in the form of NVLink 2.0 support, which promises much faster communication speeds than vanilla PCIe. An enhanced CAPI interface is also supported for accelerators that support that standard.

The accelerator story is one of the key themes of the Power9, which IBM is touting as “the premier platform for accelerated computing.” In that sense, IBM is taking a different tack than Intel, which is bringing accelerator technology on-chip and making discrete products out of them, as it has done with Xeon Phi and is in the process of doing with Altera FPGAs. By contrast, IBM has settled on the host-coprocessor model of acceleration, which offloads special-purpose processing to external devices. This has the advantage of flexibility; the Power9 can connect to virtually any type of accelerator or special-purpose coprocessor as long it speaks PCIe, CAPI or NVLink.

Understanding the IBM Power Systems Advantage

Thus the Power9 sticks with an essentially general-purpose design. As a standalone processor it is designed for mainstream datacenter applications (assuming that phrase has meaning anymore). From the perspective of floating point performance, it is about 50 percent faster than Power8, but that doesn’t make it an HPC chip, and in fact, even a mid-range Broadwell Xeon (E5-2600 V4) would likely outrun a high-end Power9 processor on Linpack. Which is fine. That’s what the GPUs and NVLink support are for.

IBM Power Systems Update 1Q17

If there is any deviation from the general-purpose theme, it’s in the direction of data-intensive workloads, especially analytics, business intelligence, and the broad category of “cognitive computing” that IBM is so fond of talking about. Here the Power processors have had something of an historical advantage in that they offered much higher memory bandwidth that their Xeon counterparts, in fact, about two to four times higher. The SO Power9 supports 120 GB/sec of memory bandwidth; the SU version, 230 GB/sec. The Power9 also comes with a very large (120 MB) L3 cache, which is built with eDRAM technology that supports speeds of up to 256 GB/sec. All of which serves to greatly lessen the memory bottleneck for data-intensive applications.

IBM Power Systems Announcement Update

According to IBM, Power9 was about 2.2 times faster for graph analytics workloads and about 1.9 times faster for business intelligence workloads. That’s on a per socket basis, comparing a 12-core Power9 to that of a 12-core Power8 at the same 4GHz clock frequency. Which is a pretty impressive performance bump from one generation to the next, although it should be pointed out that IBM offered no comparisons against the latest Broadwell Xeon chips.

The official Power roadmap from IBM does not say much in terms of timing, but thanks to the “Summit” and “Sierra” supercomputers that IBM, Nvidia, and Mellanox Technologies are building for the U.S. Department of Energy, we knew Power9 was coming out in late 2017. Here is the official Power processor roadmap from late last year:

And here is the updated one from the OpenPower Foundation that shows how compute and networking technologies will be aligned:

IBM revealed that the Power9 SO chip will be etched in the 14 nanometer process from Globalfoundries and will have 24 cores, which is a big leap for Big Blue.

That doubling of cores in the Power9 SO is a big jump for IBM, but not unprecedented. IBM made a big jump from two cores in the Power6 and Power6+ generations to eight cores with the Power7 and Power7+ generations, and we have always thought that IBM wanted to do a process shrink and get to four cores on the Power6+ and that something went wrong. IBM ended up double-stuffing processor sockets with the Power6+, which gave it an effective four-core chip. It did the same thing with certain Power5+ machines and Power7+ machines, too.

The other big change with the Power9 SO chip is that IBM is going to allow the memory controllers on the die to reach out directly and control external DDR4 main memory rather than have to work through the “Centaur” memory buffer chip that is used with the Power8 chips. This memory buffering has allowed for very high memory bandwidth and a large number of memory slots as well as an L4 cache for the processors, but it is a hassle for entry systems designs and overkill for machines with one or two sockets. Hence, it is being dropped.

The Power9 SU processor, which will be used in IBM’s own high-end NUMA machines with four or more sockets, will be sticking with the buffered memory. IBM has not revealed what the core count will be on the Power9 SU chip, but when we suggested that based on the performance needs and thermal profiles of big iron that this chip would probably have fewer cores, possibly more caches, and high clock speeds, McCredie said these were all reasonable and good guesses without confirming anything about future products.

LINUX on Power

The Power9 chips will sport an enhanced NVLink interconnect (which we think will have more bandwidth and lower latency but not more aggregate ports on the CPUs or GPUs than is available on the Power8), and we think it is possible that the Power9 SU will not have NVLink ports at all. (Although we could make a case for having a big NUMA system with lots and lots of GPUs hanging off of it using lots of NVLink ports instead of using an InfiniBand interconnect to link multiple nodes in a cluster together.)

The Power9 chip with the SMT8 cores are aimed at analytics workloads that are wrestling with lots of data, in terms of both capacity and throughput. The 24 core variant of the Power9 with SMT8 has 512 KB L2 cache memory per core, and 120 MB of L3 cache is shared across the dies in 10 MB segments with each pair of cores. The on-chip switch fabric can move data in and out of the L3 cache at 256 GB/sec, and adding in the various interconnects for memory controllers, PCI-Express 4.0 controllers, and the “Bluelink” 25 Gb/sec ports that are used to attach accelerators to the processors as well as underpinning the NVLink 2.0 protocol that will be added to next year’s “Volta” GV100 GPUs from Nvidia and IBM’s own remote SMP links for creating NUMA clusters with more than four sockets, and you have an on-chip fabric with over 7 TB/sec of aggregate bandwidth.

The Power9 chips will have 48 lanes of PCI-Express 4.0 peripheral I/O per socket, for an aggregate of 192 GB/sec of duplex bandwidth. In addition to this, the chip will support 48 lanes of 25 Gb/sec Bluelink bandwidth for other connectivity, with an aggregate bandwidth of 300 GB/sec. On the Power9 SU chips, 48 of the 25 Gb/sec lanes will be used for remote SMP links between quad-socket nodes to make a 16-socket machine, and the remaining 48 lanes of PCI-Express 4.0 will be used for PCI-Express peripherals and CAPI 2.0 accelerators. The Power9 chip has integrated 16 Gb/sec SMP links for gluelessly making the four-socket modules. In addition to the CAPI 2.0 coherent links running atop PCI-Express 4.0, there is a further enhanced CAPI protocol that runs atop the 25 Gb/sec Bluelink ports that is much more streamlined and we think is akin to something like NVM-Express for flash running over PCI-Express in that it eliminates a lot of protocol overhead from the PCI-Express bus. But that is just a hunch. It doesn’t look like the big bad boxes will be able to support this new CAPI or NVLink ports, by the way, since the Bluelink ports are eaten by NUMA expansion.

More Information:








0 reacties:

Post a Comment