The Case for a High-Level Kernel-Bypass I/O Abstraction (2019)
31 points by eventhelix 3 days ago | 15 comments
  • FridgeSeal 9 hours ago |
    This is a super cool idea, and it’s something that sounds fun to play with/try out.

    Therefore, I eagerly await the inevitable influx of:

    - “you don’t need it”

    - “you’re not FAANG enough to justify it”,

    -“seems overly complicated my Python-on-Ubuntu-is-good-enough and who needs more”

    Style comments telling us why we shouldn’t have fun things like this.

    Anyone got anymore comments to add to the bingo-card?

    • wmf 8 hours ago |
      Preemptive cynicism is even worse than regular cynicism.
    • dijksterhuis 5 hours ago |
      if you personally want to play with it, go ahead.

      i think my personal feeling is that those sorts of comments you listed come out of the woodwork more when the comments section starts turning into an "oh man, this should be the standard for everyone" kind of discussion, which is never the case and is usually the point of those kinds of replies.

      at least they are when i reply with those kinds of comments anyway

  • Gollapalli 9 hours ago |
    This is great! I think that there are a lot of latency sensitive applications which really do need to spare the kernel latency.
  • blibble 8 hours ago |
    7-10us for what is a hashtable set/get is really, really bad

    I can get a packet out to a switch and back to another machine and in 1-2us

    • gtirloni 7 hours ago |
      Do you mean 1-2ms?
      • eqvinox 7 hours ago |
        No, 1-2us is correct for that — in a datacenter, with cut-through switching.
        • gtirloni 6 hours ago |
          That's really impressive. I need to update myself on this topic. Thanks.
          • mickg10 6 hours ago |
            In reality - with decent switches at 25g - and no fec - node to node is reliably under 300ns (0.3 us)
            • davekeck 6 hours ago |
              Out of curiosity, how is that measured across machines?

              (The first thing that comes to my mind would be to use an oscilloscope with two probes, one to each machine, but I’m guessing that’s not it.)

              • toast0 an hour ago |
                Measure the round trip and divide by two for the approximate one way time. It'd be really neat to measure the time it takes for a packet to travel in one direction, but it's somewhere between hard and impossible[1]; a very short path has less room to be asymetric though.

                [1] If the clocks are synchronized, you can measure send time on one end, and receive time on the other. But synchronizing clocks involves estimating the time it takes for signals to pass im each direction, typically assuming each direction takes half the round trip.

            • publicmail 5 hours ago |
              What is the hardware involved in this test?

              Is this is with PCIe based Ethernet NICs? A single PCIe read probably takes at least a hundred nanos, right?

              Maybe I could see it with something like a busy poll pingpong over RDMA/Infiniband, but that seems really low for “traditional” networking. It’s probably not possible to even send and receive a packet via loopback device that fast.

            • znyboy 4 hours ago |
              Considering that 300 light-nanoseconds is about 90m, getting a response (or even just one-way) in that time is essentially running right at the limits of physics/causality.
        • jiggawatts 9 minutes ago |
          Meanwhile the best network I’ve ever benchmarked was AWS and measured about 55µs for a round trip!

          What on earth are you using that gets you down to single digits!?

  • joeblubaugh 7 hours ago |
    It’s really frustrating that the HotOS paper itself has no details about the benchmarking, and the blog post just says “redis benchmark”. What was the system setup? Persistence options? What was ported to demikernel? The client writing, the server reading from the NIC? Based on the problem specified in the paper, I assume its reading from the NIC that was implemented in DemiOS
  • r00tbeer 23 minutes ago |
    See https://irenezhang.net/papers/demikernel-sosp21.pdf for a more thorough paper on the Demikernel from 2021. There are some great ideas for improving the kernel interface while still allowing efficient DPDK-style pipelines.