W(h)ither POWER8

With the recent announcement that Ubuntu's ppc64le ("ppc64el") flavour is moving to require POWER9, it's worth asking not only how much life is in POWER8, but also POWER9, now that Power10 (such as it is) is now available.

POWER8 was the first OpenPOWER processor and the one planned for the original Raptor Talos (that never got released to the public), but also appeared in several third-party systems, largely by Tyan. It offered fully open firmware and while it exclusively required Centaur memory buffer chips, these could be on riser cards, interposers or even on the logic board to allow attaching regular ECC DIMMs. It introduced ISA 2.07, which among other features expanded on the vector-scalar extension instructions first introduced in POWER7 (called VSX-2 in 2.07).

POWER8 systems are certainly more widely distributed than previous generations which since about POWER5 were almost exclusively IBM, and they were also the first Power ISA CPU with a fully-functioning little-endian mode (the POWER7 implementation had gaps), which caused it to rapidly become the baseline for most distributions supporting Power. But POWER9 is even more widely distributed, not least of which because of "low end" systems like this Talos II and the Blackbird, uses 25% less power but is 50% faster than a chip that was already two to three times faster than POWER7, and has even more advantages in terms of instruction set; ISA 3.0 expands VSX further (VSX-3) and also adds a number of other useful instructions. The current incarnation of our Firefox JIT, for example, leverages new POWER9-specific instructions for remainders, accessing the program counter and 64-bit byte swapping. All this, and it's still a fully open architecture with fully open firmware.

On the other hand, Power10 is presently a step backwards. Putting its otiose binary blobs aside for the moment, there are only a few Power10 SKUs in its current infancy, none of them are workstations, and none of them don't say IBM. No Power10 hardware takes direct attach RAM, not even like the POWER8 did. No ODM has a channel for obtaining the actual CPUs. If there's a Rainier reference design to work from, no one seems to be talking about it. It's almost back to the bad old days when IBM wouldn't sell me a POWER7 and nobody else made one (my long-running POWER6 was a reseller purchase).

If Ubuntu's move is the first of many to decommission POWER8 support, that's still over six years as a first-tier citizen (almost five as second fiddle to POWER9), and no one else so far has talked about a similar move. (Even if RHEL 9 goes POWER9+ only, RHEL 8 would presumably support your POWER8 until 2029.) It's sad to see it happen but POWER9, besides being easier to get, is an improvement in virtually every way and in ways Power10 right now is not. Besides the fact IBM's still selling POWER9 machines, the chip's time on top and its wider distribution are good signs for the first Power CPU in years to be in purpose-built desktops and more third-party servers. Nearly five years atop the heap buys you a lot of market penetrance especially with a questionable successor. While all good things must come to an end, POWER8's death is hardly imminent, and POWER9's is nowhere yet in sight.


  1. I am always of the opinion that for Power 10 it is too early to draw conclusions and that it currently only makes sense for companies that have to use high-end servers and that is IBM's current plan. When IBM decides to expand the P10 offer with the lower ranges and therefore create a version of Sforza for P10 as well, then we will be able to see what possibilities there will be of using the new Power microprocessor. As for Ubuntu well, I think it's not bad that you upgrade to Power 9 at least for us, considering that all Power desktop machines are P9 based and considering it's the most popular well, an optimization of all Ubuntu software I think is a good step forward in my opinion ...

    1. My 2 cents on the matter:

      I think the step to drop POWER8 was a little premature. It doesn't outwardly seem to have been a maintenance burden, just a couple of compiler options changed when they were already optimizing for POWER9. I really can't figure out why they did it. Rumor has it they caught their POWER8 testing team completely off guard.

      As for POWER10, I think I can say quite confidently that the source code for the I/O unit and DDR4 PHY will *never* be released. They're from Synopsys and I can't think of another company more culturally averse to releasing anything. I think the best chance for POWER10 is a future new stepping with new IBM-designed PHYs for the DDR4 bridge chips and on-CPU PCIe.

      I don't see why IBM would do that though, since everyone except Raptor probably isn't too picky about the blobs. Dunno how much IBM *actually* cares about developer workstations from Raptor either. Would have been a good question for the guys in charge of porting open source software at IBM when I met them. Presumably devs don't like to port to what they can't easily test.

      I don't think direct-attach RAM will happen. It's anathema to POWER10's main concept. We might see OMI bridge chip from other vendors though, even for different kinds of RAM.


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