[Mesa-dev] [PATCH 13/16] st/nine: Rework update_vertex_buffers

[Ilia Mirkin]

On Fri, Apr 24, 2015 at 4:09 PM, Axel Davy <axel.davy at ens.fr> wrote:
> Previous code was trying to optimise to call set_vertex_buffers on
> big packets, and thus avoids as many calls as possible.
>
> However in practice doing so won't be faster (drivers implement
> set_vertex_buffers by a loop over the buffers we want to bind)
>
> When we want to unbind a buffer, we were calling set_vertex_buffers
> on a buffer with vtxbuf->buffer = NULL. It works on some drivers,
> but not on all of them, because it isn't in Gallium spec.
> This patch fixes that.
>
> Signed-off-by: Axel Davy <axel.davy at ens.fr>
> ---
>  src/gallium/state_trackers/nine/nine_state.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
>
> diff --git a/src/gallium/state_trackers/nine/nine_state.c b/src/gallium/state_trackers/nine/nine_state.c
> index 27800c6..6e01955 100644
> --- a/src/gallium/state_trackers/nine/nine_state.c
> +++ b/src/gallium/state_trackers/nine/nine_state.c
> @@ -631,7 +631,6 @@ update_vertex_buffers(struct NineDevice9 *device)
>      uint32_t mask = state->changed.vtxbuf;
>      unsigned i;
>      unsigned start;
> -    unsigned count = 0;
>
>      DBG("mask=%x\n", mask);
>
> @@ -650,18 +649,12 @@ update_vertex_buffers(struct NineDevice9 *device)
>
>      for (i = 0; mask; mask >>= 1, ++i) {

FWIW, not sure if it's faster, but you could do like

while (mask) {
  i = ffs(mask) - 1;
  ...
  mask &= ~(1 << i);
}

In practice, if all the bits tend to be consecutive starting at 0,
this will probably even be slower.

Either way, this is

Reviewed-by: Ilia Mirkin <imirkin at alum.mit.edu>

>          if (mask & 1) {
> -            if (!count)
> -                start = i;
> -            ++count;
> -        } else {
> -            if (count)
> -                pipe->set_vertex_buffers(pipe, start, count,
> -                                         &state->vtxbuf[start]);
> -            count = 0;
> +            if (state->vtxbuf[i].buffer)
> +                pipe->set_vertex_buffers(pipe, i, 1, &state->vtxbuf[i]);
> +            else
> +                pipe->set_vertex_buffers(pipe, i, 1, NULL);
>          }
>      }
> -    if (count)
> -        pipe->set_vertex_buffers(pipe, start, count, &state->vtxbuf[start]);
>
>      state->changed.vtxbuf = 0;
>  }
> --
> 2.1.0
>
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