linux-kernel - Re: [PATCH net-next v3 01/17] asm: simd context helper API

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Message-ID: <CAHmME9pmgu_xWJ0rvdS4RhzwjKPiNdkQ9nc6mqTNeb6A8xT8Eg@mail.gmail.com>
Date:   Wed, 12 Sep 2018 20:10:41 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     kevin@...rana.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Samuel Neves <sneves@....uc.pt>, linux-arch@...r.kernel.org
Subject: Re: [PATCH net-next v3 01/17] asm: simd context helper API

On Wed, Sep 12, 2018 at 8:14 AM Kevin Easton <kevin@...rana.org> wrote:
> Given that it's always supposed to be used like that, mightn't it be
> better if simd_relax() took a pointer to the context, so the call is
> just
>
>     simd_relax(&simd_context);
>
> ?
>
> The inlining means that there won't actually be a pointer dereference in
> the emitted code.
>
> If simd_put() also took a pointer then it could set the context back to
> HAVE_NO_SIMD as well?

That's sort of a neat idea. I guess in this scheme, you'd envision:

   simd_context_t simd_context;

   simd_get(&simd_context);
   simd_relax(&simd_context);
   simd_put(&simd_context);

And this way, if simd_context ever becomes a heavier struct, it can be
modified in place rather than returned by value from the function. On
the other hand, it's a little bit more annoying to type and makes it
harder to do declaration and initialization on the same line.