S01 E02
10 May 2021/01:32:56

A Requiem for SPARC with Tom Lyon

Oxide and Friends Twitter Space: May 10, 2021

A Requiem for SPARC with Tom Lyon
We’ve been holding a Twitter Space weekly on Mondays at 5p for about an hour. In addition to [@bcantrill](https://twitter.com/bcantrill) and [@ahl](https://twitter.com/ahl), speakers included special guest Tom Lyon plus Joshua Clulow, Dan McDonald, Dan Cross, Tom Killalea, Theo Schlossnagle, Antranig Vartanian, and [@perlhack](https://twitter.com/perlhack).
We recorded the space; the recording is here.
Some of the topics we hit on, in the order that we hit them:
  • [@2:06](https://youtu.be/79NNXn5Kr90?t=126) SPARC 30th anniversary dinner > SPARC was an amazing achievement for its time, > but there were some nasty trade-offs made.
  • [@2:56](https://youtu.be/79NNXn5Kr90?t=176) illumos announcement on the end of SPARC support
  • [@4:37](https://youtu.be/79NNXn5Kr90?t=277) “There is no photography allowed in the bring-up lab” story
  • [@6:23](https://youtu.be/79NNXn5Kr90?t=383) UltraSPARC-II E-cache parity error
  • [@8:51](https://youtu.be/79NNXn5Kr90?t=531) Register windows > Most people don’t know, about that first SPARC, > there was no integer multiply or divide..
    > It would trap on the instructions.
  • I feel so decadent, I’ve just been sprinkling multiplications around my code for years.
  • [@9:55](https://youtu.be/79NNXn5Kr90?t=595) popc instruction (also called Hamming Weight)
    • IBM Stretch 1961, and the one-of-a-kind IBM Harvest made for the NSA
    • Henry Warren’s 2002 Hacker’s Delight Ch. 5 shows a ~20 instruction algorithm (no branches, only adds/shifts/masks by constants) > Warren: According to computer folklore, the population count function is important to the > National Security Agency. No one (outside of NSA) seems to know just what they use it for, > but it may be in cryptography work or in searching huge amounts of material.
    • According to Agner Fog, Ice Lake performs popcnt with a 3 cycle latency, and Zen 3 with just 1 cycle latency.
    • Phil Bagwell’s 2001 Ideal Hash Trees depend on pop count > Bagwell: Note that the performance of the algorithm is seriously impacted > by the poor execution speed of the POPCT emulation in Java, a problem > the Java designers may wish to address. 
      • Persistent versions of Bagwell’s trees are used for the built-in hash maps of Clojure, and in libraries for Scala etc.
  • [@11:39](https://youtu.be/79NNXn5Kr90?t=699) This was the debate between Roger Faulkner and Jeff Bonwick: register windows
  • [@12:35](https://youtu.be/79NNXn5Kr90?t=755) Register fishing: Bryan’s version and Adam’s version > When you want to know the state of some other process, you have to flush > those register windows to memory to be able to recover the stack trace.
    • [@14:30](https://youtu.be/79NNXn5Kr90?t=870) Delay slot > We sat around the lunch table talking about how crazy it would > be to have a branch that executed right after a branch.
    • DCTI couple (delayed control transfer instruction)
    • [@15:31](https://youtu.be/79NNXn5Kr90?t=931) “Well, the instruction set doesn’t allow that..” story > Bedlam. As far as Solaris kernel discussions go, bedlam.
    • Leibniz vs. Newton
  • [@20:14](https://youtu.be/79NNXn5Kr90?t=1214) Annulled branches
  • [@22:17](https://youtu.be/79NNXn5Kr90?t=1337) Praise for SPARC
    • SPARC address space identifiers > When we were porting Solaris to x86, and deciding what fraction of the > address space would belong to the kernel vs the user, it felt disgusting to me.
  • [@25:26](https://youtu.be/79NNXn5Kr90?t=1526) Software-filled TLB > They just didn’t have the room to cram a hardware page table walk into the chip.
    • MIPS would give you a trap on a VAC conflict (virtual address cache)
  • [@27:34](https://youtu.be/79NNXn5Kr90?t=1654) It was slow, it was late, and it had a lot of problems, it was wrong.
    • UltraSPARC-III, code-named “Cheetah” > It’s weird, I compile this thing over and over, and every 80th time when > I compile and run it, it’s 40x slower..
    • UltraSPARC-IV+, code-named “Panther”
  • [@32:17](https://youtu.be/79NNXn5Kr90?t=1937) Does the Viking I-cache bug ring a bell?
    • SuperSPARC, code-named “Viking” > You’d have to DC balance the I-cache. If you had too many zeros, > they’d start flipping to ones.
    • E-cache parity error > It was due to everything but high energy particle strikes.
    • Radioactive boron in our SRAM manufacturing process
  • [@38:52](https://youtu.be/79NNXn5Kr90?t=2332) “Move it further from the tube” story > When you’re going to have a customer do something, you have to remember there’s > a human being on the other end of that. You cannot have them chasing your theories. > You need to be transparent and honest with them.
  • [@42:25](https://youtu.be/79NNXn5Kr90?t=2545) Micron DRAM story
  • [@44:38](https://youtu.be/79NNXn5Kr90?t=2678) High priced consultants and cosmic rays > They literally lined the roof with lead.. and it didn’t change the error rate at all!
  • [@46:47](https://youtu.be/79NNXn5Kr90?t=2807) And the SRAM manufacturer was..
  • [@48:11](https://youtu.be/79NNXn5Kr90?t=2891) Aftermarket
  • [@51:34](https://youtu.be/79NNXn5Kr90?t=3094) What’s that tapping sound? > Seeing how that particular sausage was made, very very slowly, was discouraging.
    • Regatta On a Chip
    • UltraSPARC-T1, code-named “Niagara” 
      • [@57:15](https://youtu.be/79NNXn5Kr90?t=3435) The only thing we could get to run fast was benchmarks..
    • “Balanced” computing
  • [@59:18](https://youtu.be/79NNXn5Kr90?t=3558) Sun Fire V880, code-named “Daktari”
  • [@1:04:14](https://youtu.be/79NNXn5Kr90?t=3854) RISC
  • [@1:06:04](https://youtu.be/79NNXn5Kr90?t=3964) Intel 432 “The only constants you need are 0 and 1”
  • [@1:09:12](https://youtu.be/79NNXn5Kr90?t=4152) Machine learning in the 80s?
  • [@1:11:37](https://youtu.be/79NNXn5Kr90?t=4297) The best historical analog for Oxide? > I loved that it was deliberate hardware-software co-design.
    • IBM AS/400 > Bill is amazing. He’s clearly the smartest person I’ve ever known. > But you never know what time scale he’s operating in, whether he’s telling you > to do something for tomorrow or for the next century.
    • Optative voice
  • [@1:14:42](https://youtu.be/79NNXn5Kr90?t=4482) How early in Sun’s history were people talking about doing their own CPU?
  • [@1:17:11](https://youtu.be/79NNXn5Kr90?t=4631) Finding SPARC bugs > I had a little Sun 4c that I had cranked up to 26k hertz, > and at 26k hertz it stopped at the banner message. > And I came in the next morning and it was at the login prompt! > This little poor machine had managed to boot! > I hit enter and it immediately panicked.
    • Processor state register (PSR), processor interrupt level (PIL)
  • [@1:20:35](https://youtu.be/79NNXn5Kr90?t=4835) OpenBoot, Forth
  • [@1:21:54](https://youtu.be/79NNXn5Kr90?t=4914) Long lived E10K, code-named “Starfire”
  • [@1:24:01](https://youtu.be/79NNXn5Kr90?t=5041) Invasive physical attacks
  • Tom Lyon and Joseph Skudlarek’s USENIX 1985 paper: All The Chips That Fit
  • Sun keyboard photo
  • [@1:29:56](https://youtu.be/79NNXn5Kr90?t=5396) The real secret of Sun’s success is that we built them to make ourselves happy. > Open source software in general, you develop it for yourself. > That way there’s at least one person who likes it.
(Did we miss anything? PRs always welcome!)
Our next Twitter Space will be on May 17th, 2021 at 5p Pacific! Join us; we always love to hear from new speakers!