[Mesa-dev] [PATCH 4/4] etnaviv: hook up linear texture sampling support

[Christian Gmeiner]

Am Mo., 21. Jan. 2019 um 10:10 Uhr schrieb Lucas Stach <l.stach at pengutronix.de>:
>
> Am Montag, den 21.01.2019, 07:50 +0100 schrieb Christian Gmeiner:
> > If the GPU supports linear sampling, linear addressing mode
> > will be used as default.
> >
> > > Signed-off-by: Christian Gmeiner <christian.gmeiner at gmail.com>
> > ---
> >  src/gallium/drivers/etnaviv/etnaviv_resource.c | 10 +++++++---
> >  src/gallium/drivers/etnaviv/etnaviv_texture.c  |  4 +++-
> >  2 files changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/src/gallium/drivers/etnaviv/etnaviv_resource.c b/src/gallium/drivers/etnaviv/etnaviv_resource.c
> > index 9a7ebf3064e..7d24b1f03bd 100644
> > --- a/src/gallium/drivers/etnaviv/etnaviv_resource.c
> > +++ b/src/gallium/drivers/etnaviv/etnaviv_resource.c
> > @@ -318,9 +318,9 @@ etna_resource_create(struct pipe_screen *pscreen,
> >  {
> >     struct etna_screen *screen = etna_screen(pscreen);
> >
> > -   /* Figure out what tiling and address mode to use -- for now, assume that
> > -    * texture cannot be linear. there is a capability LINEAR_TEXTURE_SUPPORT
> > -    * (supported on gc880 and gc2000 at least), but not sure how it works.
> > +   /* Figure out what tiling and address mode to use.
> > +    * Textures are TILED or LINEAR. If LINEAR_TEXTURE_SUPPORT capability is
> > +    * available LINEAR gets prefered.
> >      * Buffers always have LINEAR layout.
> >      */
> >     unsigned layout = ETNA_LAYOUT_LINEAR;
> > @@ -334,6 +334,10 @@ etna_resource_create(struct pipe_screen *pscreen,
> >
> >        if (util_format_is_compressed(templat->format))
> >           layout = ETNA_LAYOUT_LINEAR;
> > +      else if (VIV_FEATURE(screen, chipMinorFeatures1, LINEAR_TEXTURE_SUPPORT)) {
> > +         layout = ETNA_LAYOUT_LINEAR;
> > +         mode = ETNA_ADDRESSING_MODE_LINEAR;
> > +      }
>
> Did you do any performance measurements with this change? I don't think
> we generally want to prefer linear textures, as in theory they have
> much worse texture cache hit rates. Also a lot of the async transfer
> stuff currently depends on hitting the RS linear->tiled blit path for
> optimal performance on uploads.
>

I have not done any performance measurements yet - I only tried to get it
render correctly (piglit and amoeba) and get some feedback asap.
But I will keep an eye on perf for v2.

Regarding the async transfer staff I have the feeling that we lose the shadow
resource (etna_transfer->rsc) handling if we are using linear, which saves us
from some RS blits. Or?

> There are 2 cases where I think linear textures are useful:
>
> 1. Imported external buffers, where we might need to update the
> internal tiled copy on each resource update. Getting rid of this blit
> should help performance a good bit.
>

You are taking about etna_resource_from_handle(..). I *think* for this we
need support for linear in the pixel engine too - based on the binding flag
combinations I have seen.

> 2. 8bpp formats that can't be tiled with the RS and would hit the
> software fallback path. The tradeoff software tiling path vs. reduced
> texture cache hit rates might still prefer linear textures.
>

Yes that I something to look into.

-- 
greets
--
Christian Gmeiner, MSc

https://christian-gmeiner.info