sharkdp (u/sharkdp) - Readit News

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

fwip · 10 months ago

I've been using it for about four or five years, and never experienced this behavior.

Current defaults: "By default, it will perform at least 10 benchmarking runs and measure for at least 3 seconds." If your program takes 1s to run, it should take 10 seconds to benchmark.

Is it possible that your program was waiting for input that never came? One "gotcha" is that it expects each argument to be a full program, so if you ran `hyperfine ./a.out input.txt`, it will first bench a.out with no args, then try to bench input.txt (which will fail). If a.out reads from stdin when no argument is given, then it would hang forever, and I can see why you'd give up after a half hour.

sharkdp · 10 months ago

> Is it possible that your program was waiting for input that never came?

We do close stdin to prevent this. So you can benchmark `cat`, for example, and it works just fine.

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

Sesse__ · 10 months ago

> This is not included in the core of hyperfine, but we do have scripts to compute "advanced" statistics, and to perform t-tests here: https://github.com/sharkdp/hyperfine/tree/master/scripts

t-tests run afoul of the “no Gaussian assumptions”, though. Distributions arising from benchmarking frequently has various forms of skew which messes up t-tests and gives artificially narrow confidence intervals.

(I'll gladly give you credit for your outlier detection, though!)

>> Automatic isolation to the greatest extent possible (given appropriate permissions) > This sounds interesting. Please feel free to open a ticket if you have any ideas.

Off the top of my head, some option that would:

* Bind to isolated CPUs, if booted with it (isolcpus=) * Binding to a consistent set of cores/hyperthreads (the scheduler frequently sabotages benchmarking, especially if your cores are have very different maximum frequency) * Warns if thermal throttling is detected during the run * Warns if an inappropriate CPU governor is enabled * Locks the program into RAM (probably hard to do without some sort of help from the program) * Enables realtime priority if available (e.g., if isolcpus= is not enabled, or you're not on Linux)

Of course, sometimes you would _want_ to benchmark some of these effects, and that's fine. But most people probably won't, and won't know that they exist. I may easily have forgotten some.

On the flip side (making things more random as opposed to less), something that randomizes the initial stack pointer would be nice, as I've sometimes seen this go really, really wrong (renaming a binary from foo to foo_new made it run >1% slower!).

sharkdp · 10 months ago

> On the flip side (making things more random as opposed to less), something that randomizes the initial stack pointer would be nice, as I've sometimes seen this go really, really wrong (renaming a binary from foo to foo_new made it run >1% slower!).

This is something we do already. We set a `HYPERFINE_RANDOMIZED_ENVIRONMENT_OFFSET` environment variable with a random-length value: https://github.com/sharkdp/hyperfine/blob/87d77c861f1b6c761a...

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

Sesse__ · 10 months ago

I've only seen such things in internal tools so far, unfortunately, so if you see anything in public, please tell me :-) I'm just confused why everything thinks hyperfine is so awesome, when it does not meet what I'd consider a fairly low bar for benchmarking tools? (“Best publicly available” != “great”, in my book.)

sharkdp · 10 months ago

> “Best publicly available” != “great”

Of course. But it is free and open source. And everyone is invited to make it better.

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

Sesse__ · 10 months ago

> Hyperfine is great.

Is it, though?

What I would expect a system like this to have, at a minimum:

  * Robust statistics with p-values (not just min/max, compensation for multiple hypotheses, no Gaussian assumptions)
  * Multiple stopping points depending on said statistics.
  * Automatic isolation to the greatest extent possible (given appropriate permissions)
  * Interleaved execution, in case something external changes mid-way.

I don't see any of this in hyperfine. It just… runs things N times and then does a naïve average/min/max? At that rate, one could just as well use a shell script and eyeball the results.

sharkdp · 10 months ago

> Robust statistics with p-values (not just min/max, compensation for multiple hypotheses, no Gaussian assumptions)

This is not included in the core of hyperfine, but we do have scripts to compute "advanced" statistics, and to perform t-tests here: https://github.com/sharkdp/hyperfine/tree/master/scripts

Please feel free to comment here if you think it should be included in hyperfine itself: https://github.com/sharkdp/hyperfine/issues/523

> Automatic isolation to the greatest extent possible (given appropriate permissions)

This sounds interesting. Please feel free to open a ticket if you have any ideas.

> Interleaved execution, in case something external changes mid-way.

Please see the discussion here: https://github.com/sharkdp/hyperfine/issues/21

> It just… runs things N times and then does a naïve average/min/max?

While there is nothing wrong with computing average/min/max, this is not all hyperfine does. We also compute modified Z-scores to detect outliers. We use that to issue warnings, if we think the mean value is influenced by them. We also warn if the first run of a command took significantly longer than the rest of the runs and suggest counter-measures.

Depending on the benchmark I do, I tend to look at either the `min` or the `mean`. If I need something more fine-grained, I export the results and use the scripts referenced above.

> At that rate, one could just as well use a shell script and eyeball the results.

Statistical analysis (which you can consider to be basic) is just one reason why I wrote hyperfine. The other reason is that I wanted to make benchmarking easy to use. I use warmup runs, preparation commands and parametrized benchmarks all the time. I also frequently use the Markdown export or the JSON export to generate graphs or histograms. This is my personal experience. If you are not interested in all of these features, you can obviously "just as well use a shell script".

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

forrestthewoods · 10 months ago

No it’s not.

Back in the day my goal for Advent of Code was to run all solutions in under 1 second total. Hyperfine would take like 30 minutes to benchmark a 1 second runtime.

It was hyper frustrating. I could not find a good way to get Hyperfine to do what I wanted.

sharkdp · 10 months ago

If that's the case, I would consider it a bug. Please feel free to report it. In general, hyperfine should not take longer than ~3 seconds, unless the command itself takes > 300 ms second to run. In the latter case, we do a minimum of 10 runs by default. So if your program takes 3 min for a single iteration, it would take 30 min by default — yes. But this can be controlled using the `-m`/`--min-runs` option. You can also specify the exact amount of runs using `-r`/`--runs`, if you prefer that.

> I could not find a good way to get Hyperfine to do what I wanted

This is all documented here: https://github.com/sharkdp/hyperfine/tree/master?tab=readme-... under "Basic benchmarks". The options to control the amount of runs are also listed in `hyperfine --help` and in the man page. Please let us know if you think we can improve the documentation / discovery of those options.

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

PhilipRoman · 10 months ago

Oh that sucks, I really hate when programs impose useless shell parsing instead of letting the user give an argument vector natively.

sharkdp · 10 months ago

I don't think it's useless. You can use hyperfine to run multiple benchmarks at the same time, to get a comparison between multiple tools. So if you want it to work without quotes, you need to (1) come up with a way to separate commands and (2) come up with a way to distinguish hyperfine arguments from command arguments. It's doable, but it's also not a great UX if you have to write something like

    hyperfine -N -- ls "$dir" \; my_ls "$dir"

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

forrestthewoods · 10 months ago

The issue is it runs a kajillion tests to try and be “statistical”. But there’s no good way to say “just run it for 5 seconds and give me the best answer you can”. It’s very much designed for nanosecond to low microsecond benchmarks. Trying to fight this is trying to smash a square peg through a round hole.

sharkdp · 10 months ago

> The issue is it runs a kajillion tests to try and be “statistical”.

If you see any reason for putting “statistical” in quotes, please let us know. hyperfine does not run a lot of tests, but it does try to find outliers in your measurements. This is really valuable in some cases. For example: we can detect when the first run of your program takes much longer than the rest of the runs. We can then show you a warning to let you know that you probably want to either use some warmup runs, or a "--prepare" command to clean (OS) caches if you want a cold-cache benchmark.

> But there’s no good way to say “just run it for 5 seconds and give me the best answer you can”.

What is the "best answer you can"?

> It’s very much designed for nanosecond to low microsecond benchmarks.

Absolutely not. With hyperfine, you can not measure execution times in the "low microsecond" range, let alone nanosecond range. See also my other comment.

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

forrestthewoods · 10 months ago

Hyperfine is hyper frustrating because it only works with really really fine microsecond level benchmarks. Once you get into the millisecond range it’s worthless.

sharkdp · 10 months ago

That doesn't make a lot of sense. It's more like the opposite of what you are saying. The precision of hyperfine is typically in the single-digit millisecond range. Maybe just below 1 ms if you take special care to run the benchmark on a quiet system. Everything below that (microsecond or nanosecond range) is something that you need to address with other forms of benchmarking.

But for everything in the right range (milliseconds, seconds, minutes or above), hyperfine is well suited.

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

PhilipRoman · 10 months ago

The shell can be disabled, leaving just fork+exec

sharkdp · 10 months ago

Yes. If you don't make use of shell builtins/syntax, you can use hyperfine's `--shell=none`/`-N` option to disable the intermediate shell.

sharkdp commented on Hyperfine: A command-line benchmarking tool github.com/sharkdp/hyperf... · Posted by u/hundredwatt

mmastrac · 10 months ago

Hyperfine is a great tool but when I was using it at Deno to benchmark startup time there was a lot of weirdness around the operating system apparently caching inodes of executables.

If you are looking at shaving sub 20ms numbers, be aware you may need to pull tricks on macos especially to get real numbers.

sharkdp · 10 months ago

Caching is something that you almost always have to be aware of when benchmarking command line applications, even if the application itself has no caching behavior. Please see https://github.com/sharkdp/hyperfine?tab=readme-ov-file#warm... on how to run either warm-cache benchmarks or cold-cache benchmarks.