[musl] Re:Re: [musl] Why the musl libc did not support neon simd acceleartor officially on mem* operations?

[tugouxp <13824125580@163.com>]

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Thank you!















At 2021-08-28 17:48:47, "Markus Wichmann" <nullplan@gmx.net> wrote:
>On Sat, Aug 28, 2021 at 04:01:40PM +0800, tugouxp wrote:
>> HI guys:
>>   I found that the current implmention of musl arm port memcpy.S and
>>   other mem*.S operations did not use arm  neon instructions, this
>>   seems differenct with other counterparts like newlibc, glibc and
>>   bonic libc, which all impl. the neon version of mem* operations.
>
>I am not an expert on this or indeed anything, but it seems like there
>are two plausible explanations for this:
>
>1.) Neon support is not architectural, and not subarchitectural. It
>appears Neon comes with a new register set the kernel has to switch out
>on context switch, so Neon support is predicated on kernel support. That
>makes it a runtime thing. Leaving aside where the kernel declares such
>support, having a runtime switch in memcpy() is going to be a slowdown
>of some kind for all existing users. I don't know how much of a
>slowdown, but a slowdown nonetheless.
>
>My guess is the other libcs ignore the issue of the user compiling a
>userspace that won't run on the target platform and allow the user to
>shoot themselves in the foot.
>
>Adverting to the competition is a poor choice for this mailing list, by
>the way, because part of musl's success comes from looking at them and
>saying: No, we are not going to do that.
>
>2.) The code does not exist because it has not been written yet. You are
>welcome to submit a patch. I mean, you found the mailing list easily
>enough.
>
>
>> so could you tell me why? is there and concern about on this in musl?
>> if i want to imple my self imple. how to do this, is there any matual
>> pathches to use?
>
>None that I am aware of, so they have not been submitted to this list
>for sure.
>
>Ciao,
>Markus

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