linux-kernel - Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC

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Date:   Wed, 20 Jan 2021 20:24:29 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Arnd Bergmann <arnd@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Adrian Ratiu <adrian.ratiu@...labora.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Russell King <linux@...linux.org.uk>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Collabora Kernel ML <kernel@...labora.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning

On Wed, Jan 20, 2021 at 8:13 PM Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> On Wed, Jan 20, 2021 at 03:09:53PM -0800, Nick Desaulniers wrote:
> > So I'm thinking if we extend out this pattern to the rest of the
> > functions, we can actually avoid calls to
> > kernel_neon_begin()/kernel_neon_end() for cases in which pointers
> > would be too close to use the vectorized loop version; meaning for GCC
> > this would be an optimization (don't save neon registers when you're
> > not going to use them).  I would probably consider moving
> > include/asm-generic/xor.h somewhere under arch/arm/
> > perhaps...err...something for the other users of <asm-generic/xor.h>.
>
> We can't directly do the patch below since there are other users of the
> asm-generic/xor.h implementations than just the neon file.  If it's too
> much work to check and add __restrict everywhere, I think we'd either
> need to copy the code into the xor-neon file,

Yes; I'd rather copy that code into xor-neon, or someone under
arch/arm/ at least.

> or maybe do some ifdeffery
> so __restrict is only used for the neon version.

-- 
Thanks,
~Nick Desaulniers