[Mesa-dev] [PATCH 0/3] i965: Use intel_try_pbo_upload for sub updates and 3D textures

[Jason Ekstrand]

On Mon, Dec 22, 2014 at 7:52 PM, Kenneth Graunke <kenneth at whitecape.org>
wrote:

> On Monday, December 22, 2014 07:43:11 PM Kristian Høgsberg wrote:
> > On Mon, Dec 22, 2014 at 3:20 PM, Chris Forbes <chrisf at ijw.co.nz> wrote:
> > > Are there some performance numbers to go with this?
> >
> > Once of the synmark test cases (terrain) hits this path (pbo upload to
> > a 2d texture array) and the idea is that implementing this avoids the
> > MapTexture fallback paths.  The MapTexture paths often end up
> > stalling, doing extra copies or dirtying (setting write domain to cpu)
> > the entire texture even if we only update a part of one slice.
> >
> > As is, the patch series doesn't help that case, since we fail to blit
> > into the texture because it's too big.  Bens blitter fix over here:
> >
> >   http://cgit.freedesktop.org/~bwidawsk/mesa/log/?h=texture-array-opt
> >
> > works around the limitation by treating each slice as a separate
> > texture and with that I get a 3% speedup on IVB for the mentioned test
> > case.  On BYT the speed up is much bigger, since we avoid setting the
> > write domain to cpu for the entire 2d array texture, which avoids
> > clflushing 142mb per batch.
> >
> > I think it might be interesting to try to use meta for blitting
> > instead of the hw blitter. I have a feeling we lose performance in
> > synchronization between the two rings.
> >
> > Kristian
>
> Yes, I'd be really interested in a meta-based path - the 3D engine
> is usually much faster than the BLT these days.
>

I've been cooking up an evil scheme to do meta-based pbo upload and GPU
format conversion.  I think it would be fun to try.
--Jason
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