Date: Sat, 28 Aug 2021 22:29:18 +0800 (CST) From: tugouxp <13824125580@....com> To: musl@...ts.openwall.com Subject: Re:Re: Why the musl libc did not support neon simd acceleartor officially on mem* operations? Thank you! At 2021-08-28 17:48:47, "Markus Wichmann" <nullplan@....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 Content of type "text/html" skipped
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