linux-kernel - Re: [PATCH] drm/i915: check to see if SIMD registers are available before using SIMD

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Date:   Sun, 3 May 2020 14:35:03 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Chris Wilson <chris@...is-wilson.co.uk>
Cc:     Sebastian Siewior <bigeasy@...utronix.de>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        intel-gfx@...ts.freedesktop.org,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] drm/i915: check to see if SIMD registers are available
 before using SIMD

On Sun, May 3, 2020 at 2:30 PM Chris Wilson <chris@...is-wilson.co.uk> wrote:
>
> Quoting Jason A. Donenfeld (2020-04-30 23:10:16)
> > Sometimes it's not okay to use SIMD registers, the conditions for which
> > have changed subtly from kernel release to kernel release. Usually the
> > pattern is to check for may_use_simd() and then fallback to using
> > something slower in the unlikely case SIMD registers aren't available.
> > So, this patch fixes up i915's accelerated memcpy routines to fallback
> > to boring memcpy if may_use_simd() is false.
> >
> > Cc: stable@...r.kernel.org
>
> The same argument as on the previous submission is that we return to the
> caller if we can't use movntqda as their fallback path should be faster
> than uncached memcpy.

Oh, THAT's what you meant before. Okay, will follow up.