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

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Message-ID: <CAHmME9rMg_2eHBnfP6j9Y3O7-At90HF=ToTWeFL_Qc4nGURORg@mail.gmail.com>
Date:   Thu, 13 Sep 2018 15:52:21 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     kevin@...rana.org, Andrew Lutomirski <luto@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.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 Thu, Sep 13, 2018 at 7:03 AM Kevin Easton <kevin@...rana.org> wrote:
> Yes.  It's also how most get/put APIs already work in the kernel, eg
> kref_get/put (mostly because they tend to be 'getting/putting' an
> already-initialized object, though).

Right; in this case the object wouldn't be initialized yet, which
might defeat the purpose, since one advantage of the & way you
mentioned is _put modifies the context.

Andy - any opinions on this? The tl;dr is:

1) what we have now:

simd_context_t simd_context = simd_get();
for (item in items) {
    do_something(item);
    simd_context = simd_relax(simd_context);
}
simd_put();

2) what kevin is proposing:

simd_context_t simd_context;

simd_get(&simd_context);
for (item in items) {
    do_something(item);
    simd_relax(&simd_context);
}
simd_put(&simd_context);

I can see pros and cons of each approach.