Open Compute 'Group Hug' Board Allows Swappable CPUs In Servers

Nerval's Lobster writes "AMD, Intel, ARM: for years, their respective CPU architectures required separate sockets, separate motherboards, and in effect, separate servers. But no longer: Facebook and the Open Compute Summit have announced a common daughtercard specification that can link virtually any processor to the motherboard. AMD, Applied Micro, Intel, and Calxeda have already embraced the new board, dubbed 'Group Hug.' Hardware designs based on the technology will reportedly appear at the show. The Group Hug card will be connected via a simple x8 PCI Express connector to the main motherboard. But Frank Frankovsky, director of hardware design and supply chain operations at Facebook, also told an audience at the Summit that, while a standard has been provided, it may be some time before the real-world appearance of servers built on the technology."

Comments

huh?

[Moses48]

I don't get it. Are we redesigning the whole computer archetecture so we have a different group specing out the north bridge (etc) that all CPU manufactures will use? Or are they just adding an additional cpu into the current architecture the same way we do with graphics cards? And then offloading work onto it, like people have been doing for a while with GPGPUs?

Re:huh?

[Bengie]

It could be like what Seamicro does and use PCIe and a kind of "network switch", minus 10Gb NICs, cables, an actual switch, etc. Everything a bunch of nodes needs minus a lot of overhead.

A bunch of daughter-boards that plug into a PCIe motherboard is a great idea.

Not sure this will help an ARM system much

[Marcion]

I can understand an organisation on the scale of Facebook wanting the ability to take advantage of bargains to buy processors in bulk and swap them out. I am not sure how widely applicable this is though.

The cool thing about ARM is the lack of complexity and therefore a potentially cheaper cost and greater energy efficiency. The daughter board seems to go against that by adding complexity, if you swap out an ARM chip, which might be passively cooled or have low powered fan, with some high end Intel server chip, you will also need to change the cooling and PSU.

Why?

[hawguy]

Maybe this would be useful in some HPC environments where applications can be written to maximize the use of CPU cache, but the bandwidth of a PCI /8 or /16 slot is a fraction of what is available to a socketed CPU.

A core i7 has been clocked at 37GB/sec bandwidth, while PCIe /8 is good for 1.6GB/sec, and /16 is good for 3.2GB/sec

Is replacing the CPU socket with a PCIe card really worth giving up 90% of the memory bandwidth? I've never upgraded a CPU on a motherboard even when new generation CPU's are backwards compatible with the old motherboard since if I'm going to buy an expensive new CPU, I may as well spend the extra $75 and get a new motherboard to go along with it.

Likewise, by the time I'm ready to retire a 3 or 4 year old server in the datacenter, it's going to take more than a CPU upgrade to make it worth keeping.

Hooray for memory constrained CPU cycles?

[jandrese]

A PCIe x8 slot is pathetically slow compared to the memory channels used by CPUs today. These CPUs are going to have to be used like GPUs, sent specific workloads on specific datasets to be useful. Any kind of non-cached memory access is going to cause major thread stalls and probably kill any performance benefits.

A general purpose compute card is probably useful in cases where GPUs aren't a good fit but you want more cores per RU than you can normally get, but I see this as a niche application for the foreseeable future.

Metric racks

[Barryke]

So i just ended up on wikipedia, good grief you where not even joking about that new 21" standard. :'(
http://en.wikipedia.org/wiki/19-inch_rack#Open_Rack

19" = 48,26cm wide.
21" = 53,7cm wide.
23" = 58cm wide.
48U = 200cm high.

So 58cm 48U racks it is, dully noted.

Re:what's on the board?

[Junta]

The GbE controller may or may not be part of an IO hub which would provide USB and SATA. Also there is likely to be a video device (though ARM has video as SoC as a matter of course, Intel and AMD server chips do not have Video on package... yet....).

In a server, there is usually some service processor so that software bugs don't require a physical visit to regain capacity. In terms of manageability, I'd expect some I2C connectivity (the relation betwen fan and processor can get very interesting actually). Intel processor speaks PECI exclusively nowadays, wouldn't be surprised if standard basically forces a thermal control mechanism to terminate PECI on daughter card to speak i2c to the fan management subsystem. This is probably the greatest lost opportunity for energy savings; a wholistic system can do some pretty interesting things knowing what the fans are capable of and what sort of baffling is in place.

Also, the daughtercard undoubtedly brings the firmware with it.

All in all, the daughtercard is going to be the motherboard and not much changes. Maybe you get to reuse SATA chips, gigabit, usb and 'on-board' video chips for some cost savings on a mass upgrade, but those parts are pretty cheap and even they get dated. video, USB and gigabit might not matter for the internet datacenter of today and several tomorrows to come, but the SATA throughput is actually significant for data mining.

Backplane

[DavidYaw]

So the CPU is on the daughterboard. Everything that's specific to the CPU type (North/South bridges, etc) would have to go on there as well. Likely memory as well.

Congratulations. They've re-discovered the backplane and single board computer.