[Intel-gfx] [PATCH] drm/i915/selftests: Provide full mb() around clflush

[Rodrigo Vivi]

On Fri, Jul 06, 2018 at 09:27:47PM +0100, Chris Wilson wrote:
> Quoting Rodrigo Vivi (2018-07-06 21:23:00)
> > On Fri, Jul 06, 2018 at 06:49:26PM +0100, Chris Wilson wrote:
> > > clflush is an unserialised instruction and the IA manual strongly advises
> > > you to serialise it with a mb. To be cautious, apply one before and one
> > > after,
> > 
> > my understanding is that we need one before and one after anyways,
> > not just a matter of being cautious for being cautious..
> > 
> > Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> 
> If you are really careful, you can reduce it to a mb between writes and
> the clflush; and vice verse, the mb between clflush and subsequent
> reads. It's all about prevent the clflush from overtaking or being
> overtaken by the operations it is meant to flush or invalidate
> respectively.
> 
> But since we're being paranoid here, do both.

hm... makes sense... better to be paranoid...

> -Chris
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