[Mesa-dev] [PATCH 2/2] gallium/u_vbuf: handle indirect multidraws correctly and efficiently (v2)

[Eric Anholt]

Marek Olšák <maraeo at gmail.com> writes:

> On Fri, Jul 27, 2018 at 5:46 PM, Marek Olšák <maraeo at gmail.com> wrote:
>> On Fri, Jul 27, 2018 at 5:08 PM, Eric Anholt <eric at anholt.net> wrote:
>>> Marek Olšák <maraeo at gmail.com> writes:
>>>
>>>> From: Marek Olšák <marek.olsak at amd.com>
>>>>
>>>> v2: need to do MAX{start+count} instead of MAX{count}
>>>>     added piglit tests
>>>> ---
>>>>  src/gallium/auxiliary/util/u_vbuf.c | 199 ++++++++++++++++++++++++----
>>>>  1 file changed, 175 insertions(+), 24 deletions(-)
>>>>
>>>> diff --git a/src/gallium/auxiliary/util/u_vbuf.c b/src/gallium/auxiliary/util/u_vbuf.c
>>>> index 746ff1085ce..ca53e6218fd 100644
>>>> --- a/src/gallium/auxiliary/util/u_vbuf.c
>>>> +++ b/src/gallium/auxiliary/util/u_vbuf.c
>>>> @@ -1124,20 +1124,45 @@ static void u_vbuf_set_driver_vertex_buffers(struct u_vbuf *mgr)
>>>>     unsigned start_slot, count;
>>>>
>>>>     start_slot = ffs(mgr->dirty_real_vb_mask) - 1;
>>>>     count = util_last_bit(mgr->dirty_real_vb_mask >> start_slot);
>>>>
>>>>     pipe->set_vertex_buffers(pipe, start_slot, count,
>>>>                              mgr->real_vertex_buffer + start_slot);
>>>>     mgr->dirty_real_vb_mask = 0;
>>>>  }
>>>>
>>>> +static void
>>>> +u_vbuf_split_indexed_multidraw(struct u_vbuf *mgr, struct pipe_draw_info *info,
>>>> +                               unsigned *indirect_data, unsigned stride,
>>>> +                               unsigned draw_count)
>>>> +{
>>>> +   assert(info->index_size);
>>>> +   info->indirect = NULL;
>>>> +
>>>> +   for (unsigned i = 0; i < draw_count; i++) {
>>>> +      unsigned offset = i * stride / 4;
>>>> +
>>>> +      info->count = indirect_data[offset + 0];
>>>> +      info->instance_count = indirect_data[offset + 1];
>>>> +
>>>> +      if (!info->count || !info->instance_count)
>>>> +         continue;
>>>> +
>>>> +      info->start = indirect_data[offset + 2];
>>>> +      info->index_bias = indirect_data[offset + 3];
>>>> +      info->start_instance = indirect_data[offset + 4];
>>>> +
>>>> +      u_vbuf_draw_vbo(mgr, info);
>>>> +   }
>>>> +}
>>>> +
>>>>  void u_vbuf_draw_vbo(struct u_vbuf *mgr, const struct pipe_draw_info *info)
>>>>  {
>>>>     struct pipe_context *pipe = mgr->pipe;
>>>>     int start_vertex;
>>>>     unsigned min_index;
>>>>     unsigned num_vertices;
>>>>     boolean unroll_indices = FALSE;
>>>>     const uint32_t used_vb_mask = mgr->ve->used_vb_mask;
>>>>     uint32_t user_vb_mask = mgr->user_vb_mask & used_vb_mask;
>>>>     const uint32_t incompatible_vb_mask =
>>>> @@ -1153,47 +1178,172 @@ void u_vbuf_draw_vbo(struct u_vbuf *mgr, const struct pipe_draw_info *info)
>>>>        if (mgr->dirty_real_vb_mask & used_vb_mask) {
>>>>           u_vbuf_set_driver_vertex_buffers(mgr);
>>>>        }
>>>>
>>>>        pipe->draw_vbo(pipe, info);
>>>>        return;
>>>>     }
>>>>
>>>>     new_info = *info;
>>>>
>>>> -   /* Fallback. We need to know all the parameters. */
>>>> +   /* Handle indirect (multi)draws. */
>>>>     if (new_info.indirect) {
>>>> -      struct pipe_transfer *transfer = NULL;
>>>> -      int *data;
>>>> -
>>>> -      if (new_info.index_size) {
>>>> -         data = pipe_buffer_map_range(pipe, new_info.indirect->buffer,
>>>> -                                      new_info.indirect->offset, 20,
>>>> -                                      PIPE_TRANSFER_READ, &transfer);
>>>> -         new_info.index_bias = data[3];
>>>> -         new_info.start_instance = data[4];
>>>> -      }
>>>> -      else {
>>>> -         data = pipe_buffer_map_range(pipe, new_info.indirect->buffer,
>>>> -                                      new_info.indirect->offset, 16,
>>>> -                                      PIPE_TRANSFER_READ, &transfer);
>>>> -         new_info.start_instance = data[3];
>>>> +      const struct pipe_draw_indirect_info *indirect = new_info.indirect;
>>>> +      unsigned draw_count = 0;
>>>> +
>>>> +      /* Get the number of draws. */
>>>> +      if (indirect->indirect_draw_count) {
>>>> +         pipe_buffer_read(pipe, indirect->indirect_draw_count,
>>>> +                          indirect->indirect_draw_count_offset,
>>>> +                          4, &draw_count);
>>>> +      } else {
>>>> +         draw_count = indirect->draw_count;
>>>>        }
>>>>
>>>> -      new_info.count = data[0];
>>>> -      new_info.instance_count = data[1];
>>>> -      new_info.start = data[2];
>>>> -      pipe_buffer_unmap(pipe, transfer);
>>>> -      new_info.indirect = NULL;
>>>> -
>>>> -      if (!new_info.count)
>>>> +      if (!draw_count)
>>>>           return;
>>>> +
>>>> +      unsigned data_size = (draw_count - 1) * indirect->stride +
>>>> +                           (new_info.index_size ? 20 : 16);
>>>> +      unsigned *data = alloca(data_size);
>>>
>>> I continue to believe that alloca isn't something we should be using on
>>> unbounded data_size like this.  We should be returing GL_OUT_OF_MEMORY
>>> when we fail, not segfaulting.
>>>
>>> We're already reading back the BOs, it's not like the allocation is a
>>> performance concern at this point.
>>
>> radeonsi has optimizations where reading back BOs has no performance
>> impact other than reading from uncached memory, i.e. no sync and no
>> mmap overhead. In that case, malloc can make a difference. I agree
>> that it may be a little harder to justify considering the other things
>> that u_vbuf does.
>
> Would it be OK with you if I pushed this patch as-is with alloca?

I won't put my review/ack on it.  To use alloca responsibly, you need to
limit the maximum size you'll ask for.
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