[Intel-gfx] [PATCH v4 10/38] drm/i915: Force MMIO flips when scheduler enabled

Chris Wilson chris at chris-wilson.co.uk
Wed Jan 13 05:14:52 PST 2016

On Wed, Jan 13, 2016 at 12:37:44PM +0000, John Harrison wrote:
> On 12/01/2016 21:53, Chris Wilson wrote:
> >On Tue, Jan 12, 2016 at 03:07:03PM +0100, Daniel Vetter wrote:
> >>On Tue, Jan 12, 2016 at 11:19:26AM +0000, John Harrison wrote:
> >>>On 11/01/2016 22:16, Chris Wilson wrote:
> >>>>On Mon, Jan 11, 2016 at 06:42:39PM +0000, John.C.Harrison at Intel.com wrote:
> >>>>>From: John Harrison <John.C.Harrison at Intel.com>
> >>>>>
> >>>>>MMIO flips are the preferred mechanism now but more importantly,
> >>>>Says who?
> >>>I asked this exact question at the linux architecture forum quite some time
> >>>ago - does the scheduler need to worry about managing non-batch buffer work
> >>>such as page flips. The answer from everyone present was no, MMIO flips are
> >>>the way to go so don't over complicate the scheduler trying to support ring
> >>>flips. Indeed, execlist mode already forces MMIO flips anyway.
> >Two wrongs do not make a right, as they say. CS flips work very nicely
> >with execlists.
> They might have done at one point but if you don't test it then it
> don't work and right now it ain't being tested because:
>     static bool use_mmio_flip(struct intel_engine_cs *ring,
>               struct drm_i915_gem_object *obj)
>     ...
>         else if (i915.enable_execlists)
>             return true;

Indeed, but that is not what I have in my kernels.

Chris Wilson, Intel Open Source Technology Centre

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