On Wed, May 3, 2017 at 3:58 PM, Nicolai Hähnle <nhaeh...@gmail.com> wrote:
> From: Nicolai Hähnle <nicolai.haeh...@amd.com>
>
> Cc: mesa-sta...@lists.freedesktop.org
> ---
> src/gallium/drivers/radeonsi/si_state_draw.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/src/gallium/drivers/radeonsi/si_state_draw.c
> b/src/gallium/drivers/radeonsi/si_state_draw.c
> index e6a9ee0..3d1d1f8 100644
> --- a/src/gallium/drivers/radeonsi/si_state_draw.c
> +++ b/src/gallium/drivers/radeonsi/si_state_draw.c
> @@ -181,20 +181,34 @@ static void si_emit_derived_tess_state(struct
> si_context *sctx,
>
> /* Not necessary for correctness, but improves performance. The
> * specific value is taken from the proprietary driver.
> */
> *num_patches = MIN2(*num_patches, 40);
>
> /* SI bug workaround - limit LS-HS threadgroups to only one wave. */
> if (sctx->b.chip_class == SI) {
> unsigned one_wave = 64 / MAX2(num_tcs_input_cp,
> num_tcs_output_cp);
> *num_patches = MIN2(*num_patches, one_wave);
> +
> + if (sctx->screen->b.info.max_se == 1) {
> + /* The VGT HS block increments the patch ID
> unconditionally
> + * within a single threadgroup. This results in
> incorrect
> + * patch IDs when instanced draws are used.
> + *
> + * The intended solution is to restrict threadgroups
> to
> + * a single instance by setting SWITCH_ON_EOI, which
> + * should cause IA to split instances up. However,
> this
> + * doesn't work correctly on SI when there is no other
> + * SE to switch to.
> + */
> + *num_patches = 1;
> + }
Hi Nicolai,
This commit massively decreases tessellation performance on SI 1-SE
parts. We need a different solution. Would this work: "Set num_patches
to the greatest divisor of the the number of patches per instance."
Thanks,
Marek
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