From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: Stefan Kanthak <stefan.kanthak@nexgo.de>,
Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: libc-help@sourceware.org
Subject: Re: nextafter() about an order of magnitude slower than trivial implementation
Date: Thu, 19 Aug 2021 08:20:49 -0300 [thread overview]
Message-ID: <741b2c48-a754-51c5-cb72-a2f97795e30f@linaro.org> (raw)
In-Reply-To: <BEF317B3F18B447F8BAE9B550BE5C237@H270>
On 18/08/2021 14:11, Stefan Kanthak wrote:
> Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
>
>> The 08/16/2021 18:03, Stefan Kanthak wrote:
>>> Testing and benchmarking an exponential function that consumes
>>> about 10ns/call on an AMD EPYC 7262, I noticed that nextafter()
>>> itself is DEAD SLOW: it consumes about 8.5ns/call!
>>>
>>> The following (quick&dirty) implementation consumes 0.7ns/call,
>>> i.e. is about an order of magnitude faster:
>>
>> correctly measuring latency on a modern x86_64 core:
>>
>> musl: 3.16 ns
>> glibc: 5.68 ns
>> your: 5.72 ns
Thanks for bring this up, if you want to contribute a patch please
follow the Contribution checklist [1]. We recently dropped the
requirement of the FSF contribution, so you can use a SCO-like
license on the patches.
To change the current implementation I suggest you to also provide
a benchmark using glibc benchmark framework. Some maths functions
provide both latency and reciprocal-throughput information, and
with both numbers we can evaluate if the new implementation is
indeed better on different machines.
I would just like to ask to keep the tone respectful and be open
to suggestion and criticize, so you do not repeat the same derail
thread on musl maillist [1]. Szabolcs and Wilco did an excellent
job on some newer math functions implementation, you might read
the old thread to see how was their approach.
[1] https://sourceware.org/glibc/wiki/Contribution%20checklist
[2] https://www.openwall.com/lists/musl/2021/08/15/18
next prev parent reply other threads:[~2021-08-19 11:20 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-16 16:03 Stefan Kanthak
2021-08-18 12:51 ` Szabolcs Nagy
2021-08-18 17:11 ` Stefan Kanthak
2021-08-19 11:20 ` Adhemerval Zanella [this message]
2021-08-19 17:57 ` [PATCH] " Stefan Kanthak
2021-08-20 9:52 ` [PATCH/2nd version] " Stefan Kanthak
2021-08-20 16:55 ` Joseph Myers
2021-08-20 20:19 ` Stefan Kanthak
2021-08-20 21:03 ` Joseph Myers
2021-08-23 12:50 ` Adhemerval Zanella
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