Re: [PATCH] Re: Bignum performance (was: Shrinking the C core)

[Ihor Radchenko]

Emanuel Berg <incal@dataswamp.org> writes:

>> In practice, as more generic benchmarks demonstrated, we
>> only had 10% performance hit. Not something to claim that
>> Elisp is much slower compared to CL.
>
> What do you mean, generic +10% is a huge improvement.

It is, but it is also tangent to comparison between Elisp and CL. The
main (AFAIU) difference between Elisp and CL is in how the bignums are
stored. Elisp uses its own internal object type while CL uses GMP's
native format. And we have huge overheads converting things
back-and-forth between GMP and Elisp formats. It is by choice. And my
patch did not do anything about this difference.

Also, +10% is just on my machine. We need someone else to test things
before jumping to far-reaching conclusions. I plan to submit the patch
in a less ad-hoc state later, as a separate ticket.

>> It would be more useful to compare CL with Elisp using less
>> specialized benchmarks that do not involve bignums.
>> As Mattias commented, we do not care much about bignum
>> performance in Elisp - it is a rarely used feature; we are
>> content that it simply works, even if not fast, and the core
>> contributors (at least, Mattias) are not seeing improving
>> bignums as their priority.
>
> But didn't your patch do that already?

No. The benchmark only compared between Elisp before/after the patch.
Not with CL.

> Instead of relying on a single benchmark, one should have
> a set of benchmarks and every benchmark should have a purpose,
> this doesn't have to be so involved tho, for example "bignums"
> could be the purpose of my benchmark, so one would have
> several, say a dozen, each with the purpose of slowing the
> computer down with respect to some aspect or known
> situation that one would try to provoke ... It can be
> well-known algorithms for that matter.
>
> One would then do the same thing in CL and see, where do CL
> perform much better? The next question would be, why?

Sure. Feel free to share such benchmark for Elisp vs. CL. I only know
the benchmark library for Elisp. No equivalent comparable benchmark for
CL.

-- 
Ihor Radchenko // yantar92,
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