jkool702

> I'm curious about the performance is of forkrun "echo ." in a billion jobs vs. say pure C

Short answer: in its fastest mode, forkrun gets very close to the practical dispatch limit for this kind of workload. A tight C loop would still be faster, but at that point you're no longer comparing “parallel job dispatch”—you're comparing raw in-process execution.

Let me try and at least show what kind of performance forkrun gives here. Lets set up 1 billion newlines in a file on a tmpfs

    cd /tmp
    yes $'\n' | head -n 1000000000 > f1

now lets try frun echo

    time { frun echo <f1 >/dev/null; }

    real    0m43.779s
    user    20m3.801s
    sys     0m11.017s

forkrun in its "standard mode" hits about 25 million lines per second running newlines through a no-op (:), and ever so slightly less (23 million lines a second) running them through echo. The vast majority of this time is bash overhead. forkrun breaks up the lines into batches of (up to) 4096 (but for 1 billion lines the average batch size is probably 4095). Then for each batch, a worker-specific data-reading fd is advanced to the correct byte offset where the data starts, and the worker runs

    mapfile -t -n $N -u $fd A    # N is typically 4096 here
    echo "${A[@]}"

The second command (specifically the array expansion into a long list of quoted empty args) is what is taking up the vast majority of the time. frun has a flag (-U) then causes it to replace `"${A[@]}"` with `${A[*]}`, which (in the case of all empty inputs) collapses the long string of quoted empty args into a long list of spaces -> 0 args. This considerably speeds things up when inputs are all empty.

    time { frun -U echo <f1 >/dev/null; }

    real    0m13.295s
    user    6m0.567s
    sys     0m7.267s

And now we are at 75 million lines per second. But we are still largely limited by passing data through bash....which is why forkrun also has a mode (`-s`) where it bypasses bash mapfile + array expansion all together and instead splices (via one of the forkrun loadable builtins) data directly to the stdin of whatever you are parallelizing. If you are parallelizing a bash builtin (where there is no execve cost) forkrun gets REALLY fast.

    time { frun -s : < f1; }

    real    0m0.985s
    user    0m13.894s
    sys     0m12.398s

which means it is delimiter scanning, dynamically batching and distributing (in batches of up to 4096 lines) at a rate of OVER 1 BILLION LIONES A SECOND or at a rate of ~250,000 batches per second.

At that point the bottleneck is basically just delimiter scanning and kernel-level data movement. There’s very little “scheduler overhead” left to remove—whether you write it in bash+C hybrids (like forkrun) or pure C.

So I thought about this for a bit, and this actually doesnt surprise me all that much. This makes sense when you consider the following 2 things:

First, 14k items in batches of 100 are only 140 batches. 140 batches in 160 ms is not even 1000 batches per second. For reference, parallel tops out at around 500 per second (but is dreadfully slow) and forkrun, in its normal "passing quoted arguments via the cmdline" mode, can do about 10000 batches per second. I have no doubt rush is far more capable of distributing batches quicker than parallel, so theres a good chance that "how fast the parallelization engine can distribute work" isnt the main bottleneck for either frun nor rush for this particular workload.

Second, the way frun distributes batches is very efficient but requires setting up a substantial amount of supporting machinery. This puts (on my system) the "no-load run time" of forkrun at about 80 ms.

    time { echo | frun :; }

    real    0m0.078s
    user    0m0.027s
    sys     0m0.064s

And this 80 ms difference is pretty close to the time difference you are seeing. Id bet the "minimum no-load time" for rush is considerably lower - perhaps a couple of ms.

forkrun is optimized for plowing through MASSIVE amount of very fast running inputs...it is capable of plowing through a billion (empty) inputs a second in its fastest mode. 14k inputs just isn't enough to amortize the startup of all the lock-free machinery.

I would venture to guess that if you repeat the same test but with 100x more inputs, the relative difference between frun and rush would be considerably less.

I appreciate the high praise re: forkrun.

forkrun's NUMA approach is really largely based on the idea that, as you said, "real workloads mostly wait for memory". The waiting for memory gets worse in NUMA because accessing memory from a different chiplet or a different socket requires accessing data that is physically farther from the CPU and thus has higher latency. forkrun takes a somewhat unique approach in dealing with this: instead of taking data in, putting it somewhere, and reshuffling it around based on demand, forkrun immediately puts it on the correct numa node's memory when it comes in. This creates a NUMA-striped global data memfd. on NUMA forkrun duplicates most of its machinery (indexer+scanner+worker pool) per node, and each node's machinery is only offered chunks from the global data memfd that are already on node-local memory.

This directly aims to solve (or at least reduce the effect from) "CPUs waiting for memory" on NUMA systems, where the wait (if memory has to cross sockets) can be substantial.

Im happy to hear forkrun is working well for you!

I'll have to look into what would be required to package forkrun for the various distros. I'll try to make it happen in the near-ish future.

I hate to say it but forkrun probably wont work in cygwin. I haven't tried it, but forkrun makes heavy use of linux-only syscalls trhat I suspect arent available in cygwin.

forkrun might work under WSL2, as its my understanding WSL2 runs a full linux kernel in a hypervisor.

forkrun complements things like SLURM (and even MPI). forkrun is intra-node, and is all about utilizing all the resources any given node as efficiently as possible, including when the node has a deep NUMA topology (e.g., it's EPYC-based). This allows SLURM and MPI to focus on inter-node work distribution and coordinating who gets to run things on which node and things like that.

tl;dr: forkrun takes over the "last mile" of actually running things on a given single node, so SLURM can focus on what it does best: efficiently allocating and distributing work to different nodes across the cluster.

whoopsie...

    code_to_parallelize "$nn"

should be

    code_to_parallelize "$nn" &

The difference you are seeing in this specific usage is because frun is dynamically adjusting batch size and worker count (by default it always begins at a batch size of 1 and using 1 worker). It is pretty darn good at dynamically pinning these down pretty quickly, but with only 14k total inputs split you are probably ending up with 2-3 times as many jq calls as you do setting the batch size to 100 inputs from the start, and you may not be fully spawning 32 workers.

If you want an apples-to-apples comparison, try running the following. This tells frun to use 100 lines per batch (-l 100), to use 32 workers (-j 32). Please let me know how this one compares to the rush invocation in terms of runtime.

    printf '%s\n' 0* | frun -l 100 -j 32 -- jq -rf my_program.jq

side note: you should be able to use a space as a delimiter (-d ' ') and run

    echo 0* | frun -l 100 -j 32 -d ' ' -- jq -rf my_program.jq 

NOTE: when I posted this reply using a space as a delimiter was broken. I just pushed a PR to the forkrun main branch that fixes this. If you re-download frun.bash and source it in a new bash instance, then the above space-delimited command should work as well, and is the most direct apples-to-apples comparison to your rush command.

parallel works fine so long as the time per job is on the order of seconds or longer.

Let me give you an example of a "worst-case" scenario for parallel. Start by making a file on a tmpfs with 10 million newlines

    yes $'\n' | head -n 10000000 > /tmp/f1

So, now lets see how long it takes parallel to push all these lines through a no-op. This measures the pure "overhead of distributing 10 million lines in batches". Ill set it to use all my cpu cores (`-j $(nproc)`) and to use multiple lines per batch (`-m`).

    time { parallel -j $(nproc) -m : <f1; }

    real    2m51.062s
    user    2m52.191s
    sys     0m6.800s

Average CPU utalization here (on my 14c/28t i9-7940x) is CPU time / real time

    (172.191 + 6.8) / 171.062 = 1.0463516152 CPUs utalized

Note that there is 1 process that is pegged at 100% usage the entire time that isnt doing any "work" in terms of processing lines - its just distributing lines to workers. If we assume that thread averaged about 0.98 cores utalized, it means that throughout the run it managed to keep around 0.066 out of 28 CPUs saturated with actual work.

Now let's try with frun

    . ./frun.bash
    time { frun : <f1; }

    real    0m0.559s
    user    0m10.409s
    sys     0m0.201s

CPU utilization is

    ( 10.409 + .201 ) / .559 = 18.9803220036 CPUs utalized

Lets compare the wall clock times

    171.062 / 0.559 = 306x speedup

Interestingly, if we look at the ratio of CPU utilization (spent on real work):

    18.9803220036 / 0.066 = 287x more CPU usage doing actual work

which gives a pretty straightforward story - forkrun is 300x faster here because it is utilizing 300x more CPU for actually doing work.

This regime of "high frequency low latency tasks" - millions or billions of tasks that make milliseconds or microseconds each - is the regime where forkrun excels and tools like parallel fall apart.

Side note: if I bump it to 100 million newlines:

    time { frun : <f1; }

    real    0m4.212s
    user    1m52.397s
    sys     0m1.019s

CPU utilization:

    ( 112.397 + 1.019 ) / 4.212 = 26.9268 CPUs utalized

which on a 14c/28t CPU doing no-ops...isnt bad.

> And if you’re objective, what could be done to other tools to make them competitive?

I wanted to reply separately to this bit, because I needed a bit of time to think about and respond to it.

To be frank, parallel optimizes for "breadth of features" and has, for example, the ability to coordinate distributed computing over ssh. But it fundamentally assumes that the workload itself will take dramatically longer than the coordination.

To really be competitive in "high-frequency low-latency workloads", where you have millions of inputs and each only takes microseconds, you would need a complete rewrite with an entirely different way of thinking.

Let me drop a few numbers just to drive this point home. Parallel is capable of batching and distributing around 500 batches of work a second. forkrun, in its "pass arguments via quoted cmdline args" mode is capable of batching and distributing around 10,000 batches a second. This is mostly limited by how fast bash can assemble long strings of quoted arguments to pass via the command line. In forkrun's `-s` mode, which bypasses bash entirely and splices data directly to the stdin of what you are parallelizing, forkrun is capable of batching and distributing over 200,000 batches a second.

The biggest architectural hurdle most existing tools have that makes it impossible to achieve forkrun's batch distribution rate is that almost all use a central distributor thread that forks each individual call (which is very expensive) and that is ALWAYS the bottleneck in high-frequency low-latency workloads. Pushing past this requires moving to a persistent worker model without a central coordinator. This alone necessitates a complete rewrite for basically all the existing tools.

That said, forkrun takes it so much further:

* It uses a SIMD-accelerated delimiter scanner + lock-free async-io to allow for workers to not only execute in parallel but to read inputs to run in parallel.

* It doesn't just use a standard "lock-free" design with CAS retry loops everywhere - it treats the problem like a physical pipeline of data flow and structurally eliminates contention between workers. The literal only "contention" is a single atomic on a single cache line - namely when a worker claims a batch by running `atomic_fetch_add` on a global monotonically increasing index (`read_idx`).

* It doesn't use heuristics - it uses a proper closed-loop control system. There is a 3-stage ramp-up (saturate workers -> geometric ramp -> backpressure-guided PID) to dynamically determine the batch size and the number of workers that works extremely well for all input types with 0 manual tuning.

* It keeps complexity in the slow path. Claiming a batch of lines literally just involves reading a couple shared mmap'ed vars and an `atomic_fetch_add` op in the fast path, which is why it can break 1 billion lines a second. The complexity is all so the slow path degrades gracefully, which is where it smartly trades latency for throughput (but only when throughput is limited by stdin to begin with).

* It treats NUMA as 1st class and chooses the "obvious in hindsight" path to just put data on the correct NUMA node from the very start instead of re-shuffling it between nodes reactively later.

I could go on, but the TL;DR is: to be competitive, other tools would really need to try and solve the "high-frequency low-latency stream parallelization" problem from first principles like forkrun did.

10 years represents going from

    maxJobs=$(nprocs)
    while read -r nn; do
      code_to_parallelize "$nn"
      (( $(jobs -p | wc -l) > maxJobs )) && wait -n
    done < inputs

to a NUMA-Aware Contention-Free Dynamically-Auto-Tuning Bash-Native Streaming Parallelization Engine. I dare say 10 years is about the norm for going from "beginner" to "PhD-level" work.

> I ask because I see multiple em dashes in your description here, and a lot of no X, no Y... notation that Codex seems to be fond of.

I asked a few LLM's for tips on writing the HN post. The post is my own words, but their style may have rubbed off on me a little bit. I'm admittedly better at the technical aspects than I am at "writing good catchy posts that dont turn into 20 pages of technical writing", so...

curl isnt required - you just need to source the `frun.bash` file. Downloading frun.bash and sourcing it works just fine. directly sourcing a curl stream that grabs frun.bash from the github repo is just an alternate approach. It is not "required" by any means.

How did it work for you?