[Mesa-dev] [PATCH 2/2] i965/gen6/gs: Handle case where a GS doesn't allocate VUE

andrey simiklit asimiklit.work at gmail.com
Thu Jun 21 13:27:52 UTC 2018


HI all,

Sorry, just ignore this patch with incorrect subject.
I will send correct one shortly.

Regards,
Andrii.

On Thu, Jun 21, 2018 at 4:12 PM, Andrii Simiklit <asimiklit.work at gmail.com>
wrote:

> We can not use the VUE Dereference flags combination for EOT
> message under ILK and SNB because the threads are not initialized
> there with initial VUE handle unlike Pre-IL.
> So to avoid GPU hangs on SNB and ILK we need
> to avoid usage of the VUE Dereference flags combination.
> (Was tested only on SNB but according to the specification
> SNB Volume 2 Part 1: 1.6.5.3, 1.6.5.6
> the ILK must behave itself in the similar way)
>
> v2: Approach to fix this issue was changed.
> Instead of different EOT flags in the program end
> we will create VUE every time even if GS produces no output.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105399
>
> Signed-off-by: Andrii Simiklit <andrii.simiklit at globallogic.com>
> ---
>  src/intel/compiler/gen6_gs_visitor.cpp | 88
> +++++++++-------------------------
>  1 file changed, 23 insertions(+), 65 deletions(-)
>
> diff --git a/src/intel/compiler/gen6_gs_visitor.cpp
> b/src/intel/compiler/gen6_gs_visitor.cpp
> index ac3ba55..b831d33 100644
> --- a/src/intel/compiler/gen6_gs_visitor.cpp
> +++ b/src/intel/compiler/gen6_gs_visitor.cpp
> @@ -300,11 +300,10 @@ gen6_gs_visitor::emit_urb_write_opcode(bool
> complete, int base_mrf,
>        /* Otherwise we always request to allocate a new VUE handle. If
> this is
>         * the last write before the EOT message and the new handle never
> gets
>         * used it will be dereferenced when we send the EOT message. This
> is
> -       * necessary to avoid different setups (under Pre-IL only) for the
> EOT message (one for the
> +       * necessary to avoid different setups for the EOT message (one for
> the
>         * case when there is no output and another for the case when there
> is)
>         * which would require to end the program with an IF/ELSE/ENDIF
> block,
> -       * something we do not want.
> -       * But for ILK and SNB we can not avoid the end the program with an
> IF/ELSE/ENDIF block.
> +       * something we do not want.
>         */
>        inst = emit(GS_OPCODE_URB_WRITE_ALLOCATE);
>        inst->urb_write_flags = BRW_URB_WRITE_COMPLETE;
> @@ -351,27 +350,27 @@ gen6_gs_visitor::emit_thread_end()
>     int max_usable_mrf = FIRST_SPILL_MRF(devinfo->gen);
>
>     /* Issue the FF_SYNC message and obtain the initial VUE handle. */
> -   emit(CMP(dst_null_ud(), this->vertex_count, brw_imm_ud(0u),
> BRW_CONDITIONAL_G));
> -   emit(IF(BRW_PREDICATE_NORMAL));
> -   {
> -      this->current_annotation = "gen6 thread end: ff_sync";
> +   this->current_annotation = "gen6 thread end: ff_sync";
>
> -      vec4_instruction *inst;
> -      if (prog->info.has_transform_feedback_varyings) {
> +   vec4_instruction *inst = NULL;
> +   if (prog->info.has_transform_feedback_varyings) {
>           src_reg sol_temp(this, glsl_type::uvec4_type);
>           emit(GS_OPCODE_FF_SYNC_SET_PRIMITIVES,
> -              dst_reg(this->svbi),
> -              this->vertex_count,
> -              this->prim_count,
> -              sol_temp);
> +               dst_reg(this->svbi),
> +               this->vertex_count,
> +               this->prim_count,
> +               sol_temp);
>           inst = emit(GS_OPCODE_FF_SYNC,
>                       dst_reg(this->temp), this->prim_count, this->svbi);
> -      } else {
> +   } else {
>           inst = emit(GS_OPCODE_FF_SYNC,
>                       dst_reg(this->temp), this->prim_count,
> brw_imm_ud(0u));
> -      }
> -      inst->base_mrf = base_mrf;
> +   }
> +   inst->base_mrf = base_mrf;
>
> +   emit(CMP(dst_null_ud(), this->vertex_count, brw_imm_ud(0u),
> BRW_CONDITIONAL_G));
> +   emit(IF(BRW_PREDICATE_NORMAL));
> +   {
>        /* Loop over all buffered vertices and emit URB write messages */
>        this->current_annotation = "gen6 thread end: urb writes init";
>        src_reg vertex(this, glsl_type::uint_type);
> @@ -415,7 +414,7 @@ gen6_gs_visitor::emit_thread_end()
>                 dst_reg reg = dst_reg(MRF, mrf);
>                 reg.type = output_reg[varying][0].type;
>                 data.type = reg.type;
> -               vec4_instruction *inst = emit(MOV(reg, data));
> +               inst = emit(MOV(reg, data));
>                 inst->force_writemask_all = true;
>
>                 mrf++;
> @@ -450,11 +449,8 @@ gen6_gs_visitor::emit_thread_end()
>        if (prog->info.has_transform_feedback_varyings)
>           xfb_write();
>     }
> -   const bool common_eot_approach_can_be_used = (devinfo->gen < 5);
> -   if(common_eot_approach_can_be_used)
> -   {
> -      emit(BRW_OPCODE_ENDIF);
> -   }
> +   emit(BRW_OPCODE_ENDIF);
> +
>     /* Finally, emit EOT message.
>      *
>      * In gen6 we need to end the thread differently depending on whether
> we have
> @@ -464,35 +460,11 @@ gen6_gs_visitor::emit_thread_end()
>      *
>      * However, this would lead us to end the program with an ENDIF opcode,
>      * which we want to avoid, so what we do is that we always request a
> new
> -    * VUE handle every time we do a URB WRITE, even for the last vertex
> we emit.
> +    * VUE handle every time, even if GS produces no output.
>      * With this we make sure that whether we have emitted at least one
> vertex
>      * or none at all, we have to finish the thread without writing to the
> URB,
> -    * which works for both cases (but only under Pre-IL) by setting
> -    * the COMPLETE and UNUSED flags in the EOT message.
> -    *
> -    * But under ILK or SNB we must not use combination COMPLETE and
> UNUSED
> -    * because this combination could be used only for already allocated
> VUE.
> -    * But unlike Pre-IL in the ILK and SNB
> -    * the initial VUE is not passed to threads.
> -    * This behaver mentioned in specification:
> -    * SNB Volume 2 Part 1:
> -    *  "1.6.5.3 VUE Allocation (GS, CLIP) [DevIL]"
> -    *  "1.6.5.4 VUE Allocation (GS) [DevSNB+]"
> -    *     "The threads are not passed an initial handle.
> -    *     Instead, they request a first handle (if any)
> -    *     via the URB shared function’s FF_SYNC message (see Shared
> Functions).
> -    *     If additional handles are required,
> -    *     the URB_WRITE allocate mechanism (mentioned above) is used."
> -    *
> -    * So for ILK and for SNB we must use only UNUSED flag.
> -    * This is accepteble combination according to:
> -    *    SNB Volume 4 Part 2:
> -    *       "2.4.2 Message Descriptor"
> -    *          "Table lists the valid and invalid combinations of
> -    *           the Complete, Used, Allocate and EOT bits"
> -    *          "Thread terminate non-write of URB"
> -    *    SNB Volume 2 Part 1:
> -    *       "1.6.5.6 Thread Termination"
> +    * which works for both cases by setting the COMPLETE and UNUSED flags
> in
> +    * the EOT message.
>      */
>     this->current_annotation = "gen6 thread end: EOT";
>
> @@ -504,26 +476,12 @@ gen6_gs_visitor::emit_thread_end()
>        emit(GS_OPCODE_SET_DWORD_2, dst_reg(MRF, base_mrf), data);
>     }
>
> -   vec4_instruction *inst = emit(GS_OPCODE_THREAD_END);
> +   inst = emit(GS_OPCODE_THREAD_END);
>     inst->urb_write_flags = BRW_URB_WRITE_COMPLETE | BRW_URB_WRITE_UNUSED;
>     inst->base_mrf = base_mrf;
>     inst->mlen = 1;
> -
> -   if(!common_eot_approach_can_be_used)
> -   {
> -      emit(BRW_OPCODE_ELSE);
> -
> -      this->current_annotation = "gen6 thread end: EOT";
> -
> -      vec4_instruction *unused_urb_inst = emit(GS_OPCODE_THREAD_END);
> -      unused_urb_inst->urb_write_flags = BRW_URB_WRITE_UNUSED;
> -      unused_urb_inst->base_mrf = base_mrf;
> -      unused_urb_inst->mlen = 1;
> -
> -      emit(BRW_OPCODE_ENDIF);
> -   }
>  }
> -
> +
>  void
>  gen6_gs_visitor::setup_payload()
>  {
> --
> 2.7.4
>
>
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