diff options
authorOded Gabbay <>2015-11-03 10:36:01 +0200
committerRoland Scheidegger <>2015-11-04 02:38:53 +0100
commit39b4dfe6ab1003863778a25c091c080e098833ec (patch)
parent59bbe2681b73c3795b7298e2486d5fde7c464ed5 (diff)
llvmpipe: use simple coeffs calc for 128bit vectors
There are currently two methods in llvmpipe code to calculate coeffs to be used as inputs for the fragment shader. The two methods use slightly different ways to do the floating point calculations and thus produce slightly different results. The decision which method to use is determined by the size of the vector that is used by the platform. For vectors with size of more than 128bit, a single-step method is used, in which coeffs_init_simple() + attribs_update_simple() are called. For vectors with size of 128bit or less, a two-step method is used, in which coeffs_init() + attribs_update() are called. This causes some piglit tests (clip-distance-bulk-copy, interface-vs-unnamed-to-fs-unnamed) to fail when using platforms with 128bit vectors (such as ppc64le or x86-64 without AVX). This patch makes platforms with 128bit vectors use the single-step method (aka "simple" method) instead of the two-step method. This would make the resulting coeffs identical between more platforms, make sure the piglit tests passes, and make debugging and maintainability a bit easier as the generated LLVM IR will be the same for more platforms. The performance impact is negligible for x86-64 without AVX, and basically non-existent for ppc64le, as it can be seen from the following benchmarking results: - glxspheres, on ppc64le: - original code: 4.892745317 frames/sec 5.460303857 Mpixels/sec - with the patch: 4.932083873 frames/sec 5.504205571 Mpixels/sec - Additional 0.8% performance boost - glxspheres, on x86-64 without AVX: - original code: 20.16418809 frames/sec 22.50323395 Mpixels/sec - with the patch: 20.31328989 frames/sec 22.66963152 Mpixels/sec - Additional 0.74% performance boost - glmark2, on ppc64le: - original code: score of 58 - with my change: score of 57 - glmark2, on x86-64 without AVX: - original code: score of 175 - with the patch: score of 167 - Impact of of -4.5% on performance - OpenArena, on ppc64le: - original code: 3398 frames 1719.0 seconds 2.0 fps 255.0/505.9/2773.0/0.0 ms - with the patch: 3398 frames 1690.4 seconds 2.0 fps 241.0/497.5/2563.0/0.2 ms - 29 seconds faster with the patch, which is about 2% - OpenArena, on x86-64 without AVX: - original code: 3398 frames 239.6 seconds 14.2 fps 38.0/70.5/719.0/14.6 ms - with the patch: 3398 frames 244.4 seconds 13.9 fps 38.0/71.9/697.0/14.3 ms - 0.3 fps slower with the patch (about 2%) Additional details can be found at: Signed-off-by: Oded Gabbay <> Reviewed-by: Roland Scheidegger <>
1 files changed, 6 insertions, 1 deletions
diff --git a/src/gallium/drivers/llvmpipe/lp_bld_interp.c b/src/gallium/drivers/llvmpipe/lp_bld_interp.c
index df262fa471..ceac86abe1 100644
--- a/src/gallium/drivers/llvmpipe/lp_bld_interp.c
+++ b/src/gallium/drivers/llvmpipe/lp_bld_interp.c
@@ -746,7 +746,12 @@ lp_build_interp_soa_init(struct lp_build_interp_soa_context *bld,
pos_init(bld, x0, y0);
- if (coeff_type.length > 4) {
+ /*
+ * Simple method (single step interpolation) may be slower if vector length
+ * is just 4, but the results are different (generally less accurate) with
+ * the other method, so always use more accurate version.
+ */
+ if (1) {
bld->simple_interp = TRUE;
/* XXX this should use a global static table */