[Mesa-dev] [PATCH v2 3/3] i965/gen9: Add workarounds for object preemption.

[Kenneth Graunke]

On Monday, October 29, 2018 10:19:54 AM PDT Rafael Antognolli wrote:
> Gen9 hardware requires some workarounds to disable preemption depending
> on the type of primitive being emitted.
> 
> We implement this by adding a new atom that tracks BRW_NEW_PRIMITIVE.
> Whenever it happens, we check the current type of primitive and
> enable/disable object preemption.
> 
> For now, we just ignore blorp.  The only primitive it emits is
> 3DPRIM_RECTLIST, and since it's not listed in the workarounds, we can
> safely leave preemption enabled when it happens. Or it will be disabled
> by a previous 3DPRIMITIVE, which should be fine too.
> 
> Signed-off-by: Rafael Antognolli <rafael.antognolli at intel.com>
> Cc: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/mesa/drivers/dri/i965/genX_state_upload.c | 47 +++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/src/mesa/drivers/dri/i965/genX_state_upload.c b/src/mesa/drivers/dri/i965/genX_state_upload.c
> index 740cb0c4d2e..3a01bab1ae1 100644
> --- a/src/mesa/drivers/dri/i965/genX_state_upload.c
> +++ b/src/mesa/drivers/dri/i965/genX_state_upload.c
> @@ -5563,6 +5563,50 @@ static const struct brw_tracked_state genX(blend_constant_color) = {
>  
>  /* ---------------------------------------------------------------------- */
>  
> +#if GEN_GEN == 9
> +
> +/**

 * Enable or disable preemption based on the current primitive type.
 * (This should only be necessary on Gen9 hardware, not Gen10+.)
 *

> + * Implement workarounds for preemption:
> + *    - WaDisableMidObjectPreemptionForGSLineStripAdj
> + *    - WaDisableMidObjectPreemptionForTrifanOrPolygon
> + */
> +static void
> +gen9_emit_preempt_wa(struct brw_context *brw)
> +{

I think this might be a bit easier to follow as

   bool object_preemption = true;

   if (brw->primitive == _3DPRIM_LINESTRIP_ADJ && brw->gs.enabled)
      object_preemption = false;

   if (brw->primitive == _3DPRIM_TRIFAN)
      object_preemption = false;

   brw_enable_obj_preemption(brw, object_preemption);

(with the comments of course.)

Do we need any stalling when whacking CS_CHICKEN1...?

Looking through the workarounds list, I believe that we also need to
disable mid-object preemption for _3DPRIM_LINELOOP (Gen9 WA #0816).

We may need to disable it if instance_count > 0 in the 3DPRIMITIVE
(Gen9 WA #0798).

We may also need to disable autostripping by whacking some chicken
registers if it's enabled (Gen9 WA #0799).  Which would be lame,
because that's likely a useful optimization.  I guess we could disable
preemption for TRILIST and LINELIST as well to be safe.

And GPGPU preemption looks like a mile long list of workarounds,
so let's not try it on Gen9.

> +   /* WaDisableMidObjectPreemptionForGSLineStripAdj
> +    *
> +    *    WA: Disable mid-draw preemption when draw-call is a linestrip_adj and
> +    *    GS is enabled.
> +    */
> +   bool object_preemption =
> +      !(brw->primitive == _3DPRIM_LINESTRIP_ADJ && brw->gs.enabled);
> +
> +   /* WaDisableMidObjectPreemptionForTrifanOrPolygon
> +    *
> +    *    TriFan miscompare in Execlist Preemption test. Cut index that is on a
> +    *    previous context. End the previous, the resume another context with a
> +    *    tri-fan or polygon, and the vertex count is corrupted. If we prempt
> +    *    again we will cause corruption.
> +    *
> +    *    WA: Disable mid-draw preemption when draw-call has a tri-fan.
> +    */
> +   object_preemption =
> +      object_preemption && !(brw->primitive == _3DPRIM_TRIFAN);
> +
> +   brw_enable_obj_preemption(brw, object_preemption);
> +}
> +
> +static const struct brw_tracked_state gen9_preempt_wa = {
> +   .dirty = {
> +      .mesa = 0,
> +      .brw = BRW_NEW_PRIMITIVE | BRW_NEW_GEOMETRY_PROGRAM,
> +   },
> +   .emit = gen9_emit_preempt_wa,
> +};
> +#endif
> +
> +/* ---------------------------------------------------------------------- */
> +
>  void
>  genX(init_atoms)(struct brw_context *brw)
>  {
> @@ -5867,6 +5911,9 @@ genX(init_atoms)(struct brw_context *brw)
>  
>        &genX(cut_index),
>        &gen8_pma_fix,
> +#if GEN_GEN == 9
> +      &gen9_preempt_wa,
> +#endif
>     };
>  #endif
>  
> 

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: This is a digitally signed message part.
URL: <https://lists.freedesktop.org/archives/mesa-dev/attachments/20181030/b5846d3c/attachment.sig>