[Intel-gfx] [PATCH v5 09/35] drm/i915: Force MMIO flips when scheduler enabled

Chris Wilson chris at chris-wilson.co.uk
Sat Feb 20 09:22:14 UTC 2016

On Fri, Feb 19, 2016 at 11:28:05AM -0800, Jesse Barnes wrote:
> On 02/18/2016 06:26 AM, John.C.Harrison at Intel.com wrote:
> > From: John Harrison <John.C.Harrison at Intel.com>
> > 
> > MMIO flips are the preferred mechanism now

Because introducing variable latency in waking up a big core is a good

> but more importantly, pipe
> > based flips cause issues for the scheduler. Specifically, submitting
> > work to the rings around the side of the scheduler could cause that
> > work to be lost if the scheduler generates a pre-emption event on that
> > ring.

No. That is just incredibily bad design.

> Why can't we use mmio flips unconditionally?  Maarten or Ville?

Why would we want to? CS flips work just fine in execlists and no reason
was ever given as to why they were not enabled, just laziness.

Chris Wilson, Intel Open Source Technology Centre

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