[igt-dev] [PATCH i-g-t v3 1/2] lib/igt_fb: Don't use blitter for large buffers

[Chris Wilson]

Quoting Ville Syrjälä (2019-04-09 13:25:55)
> On Mon, Apr 08, 2019 at 06:20:50PM +0100, Chris Wilson wrote:
> > Quoting Chris Wilson (2019-04-08 18:19:26)
> > > Quoting Ville Syrjala (2019-04-08 18:13:06)
> > > > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > > 
> > > > The blitter stride is limited to <32k. Fall back to gtt mmap or
> > > > rendercopy if we're about to exceed that.
> > > > 
> > > > Not quite sure why we're not just using gtt mmap for Y tiling
> > > > always. But let's keep it like that for now.
> > > > 
> > > > v2: Use rendercopy as the fallback for Yf
> > > > v3: Deal with gen4+ tiled stride correctly (Chris)
> > > > 
> > > > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > > > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > > > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > > ---
> > > >  lib/igt_fb.c | 36 +++++++++++++++++++++++++++++-------
> > > >  1 file changed, 29 insertions(+), 7 deletions(-)
> > > > 
> > > > diff --git a/lib/igt_fb.c b/lib/igt_fb.c
> > > > index 6adf422228e8..d2f756dba2e9 100644
> > > > --- a/lib/igt_fb.c
> > > > +++ b/lib/igt_fb.c
> > > > @@ -1576,6 +1576,31 @@ struct fb_blit_upload {
> > > >         struct intel_batchbuffer *batch;
> > > >  };
> > > >  
> > > > +static int max_blitter_stride(int fd, uint64_t modifier)
> > > > +{
> > > > +       int stride = 32768;
> > > > +
> > > > +       if (intel_gen(intel_get_drm_devid(fd)) >= 4 &&
> > > > +           modifier != DRM_FORMAT_MOD_NONE)
> > > 
> > > * fingers crossed that the modifier is the single truth
> > > 
> > > > +               stride *= 4;
> > > > +
> > > > +       return stride;
> > > > +}
> > > > +
> > > > +static bool use_rendercopy(const struct igt_fb *fb)
> > > > +{
> > > > +       return is_ccs_modifier(fb->modifier) ||
> > > > +               (fb->modifier == I915_FORMAT_MOD_Yf_TILED &&
> > > > +                fb->strides[0] >= max_blitter_stride(fb->fd, fb->modifier));
> > > > +}
> > > > +
> > > > +static bool use_blitter(const struct igt_fb *fb)
> > > > +{
> > > > +       return (fb->modifier == I915_FORMAT_MOD_Y_TILED ||
> > > > +               fb->modifier == I915_FORMAT_MOD_Yf_TILED) &&
> > 
> > Oh but you would prefer to use rendercopy for Y_TILED (not just
> > Yf_TILED). The blitter does work with Y_TILED, but it is quite slow.
> 
> Or we could just switch Y tiled to always use gtt mmap?

We could, just make sure to use memcpy_from_wc to speed it up. Although
GTT is on the way out, I doubt it affects these use cases.

> I'm not sure why it wants to use the blitter. Some historical
> reason I presume.

Having redundant methods available is not a bad thing when we want to
cross-check.
-Chris