On 12 August 2016 at 16:07, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> ---
> 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?
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