netdev - Re: [PATCH v2 01/17] asm: simd context helper API

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Message-ID: <alpine.DEB.2.21.1809061542330.1570@nanos.tec.linutronix.de>
Date:   Thu, 6 Sep 2018 15:42:44 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
cc:     Andrew Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Neves <sneves@....uc.pt>, linux-arch@...r.kernel.org,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v2 01/17] asm: simd context helper API

On Sat, 1 Sep 2018, Jason A. Donenfeld wrote:
> On Sat, Sep 1, 2018 at 2:32 PM Andy Lutomirski <luto@...nel.org> wrote:
> > I tend to think the right approach is to merge Jason's code and then
> > make it better later.  Even with a totally perfect lazy FPU restore
> > implementation on x86, we'll probably still need some way of dealing
> > with SIMD contexts.  I think we're highly unlikely to ever a allow
> > SIMD usage in all NMI contexts, for example, and there will always be
> > cases where we specifically don't want to use all available SIMD
> > capabilities even if we can.  For example, generating random numbers
> > does crypto, but we probably don't want to do *SIMD* crypto, since
> > that will force a save and restore and will probably fire up the
> > AVX512 unit, and that's not worth it unless we're already using it for
> > some other reason.
> >
> > Also, as Rik has discovered, lazy FPU restore is conceptually
> > straightforward but isn't entirely trivial :)
> 
> Sounds good. I'll move ahead on this basis.

Fine with me.