[Intel-gfx] [PATCH 6/9] drm/i915/cmdparser: Compare against the previous command descriptor

[Matthew Auld]

On 12 August 2016 at 16:07, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On the blitter (and in test code), we see long sequences of repeated
> commands, e.g. XY_PIXEL_BLT, XY_SCANLINE_BLT, or XY_SRC_COPY. For these,
> we can skip the hashtable lookup by remembering the previous command
> descriptor and doing a straightforward compare of the command header.
> The corollary is that we need to do one extra comparison before lookup
> up new commands.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_cmd_parser.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
> index 274f2136a846..3b1100a0e0cb 100644
> --- a/drivers/gpu/drm/i915/i915_cmd_parser.c
> +++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
> @@ -350,6 +350,9 @@ static const struct drm_i915_cmd_descriptor hsw_blt_cmds[] = {
>         CMD(  MI_LOAD_SCAN_LINES_EXCL,          SMI,   !F,  0x3F,   R  ),
>  };
>
> +static const struct drm_i915_cmd_descriptor noop_desc =
> +       CMD(MI_NOOP, SMI, F, 1, S);
> +
>  #undef CMD
>  #undef SMI
>  #undef S3D
> @@ -898,11 +901,14 @@ find_cmd_in_table(struct intel_engine_cs *engine,
>  static const struct drm_i915_cmd_descriptor*
>  find_cmd(struct intel_engine_cs *engine,
>          u32 cmd_header,
> +        const struct drm_i915_cmd_descriptor *desc,
>          struct drm_i915_cmd_descriptor *default_desc)
>  {
> -       const struct drm_i915_cmd_descriptor *desc;
>         u32 mask;
>
> +       if (((cmd_header ^ desc->cmd.value) & desc->cmd.mask) == 0)
> +               return desc;
> +
>         desc = find_cmd_in_table(engine, cmd_header);
>         if (desc)
>                 return desc;
> @@ -911,10 +917,10 @@ find_cmd(struct intel_engine_cs *engine,
>         if (!mask)
>                 return NULL;
>
> -       BUG_ON(!default_desc);
Why remove this, was it overkill?

> -       default_desc->flags = CMD_DESC_SKIP;
> +       default_desc->cmd.value = cmd_header;
> +       default_desc->cmd.mask = 0xffff0000;
Where did you pluck this mask from?