[Mesa-dev] [PATCH v2 5/7] anv/pipeline: Be smarter about depth/stencil state
Nanley Chery
nanleychery at gmail.com
Fri Feb 10 23:18:03 UTC 2017
On Fri, Feb 10, 2017 at 02:55:42PM -0800, Nanley Chery wrote:
> On Fri, Feb 10, 2017 at 11:02:19AM -0800, Jason Ekstrand wrote:
> > It's a bit hard to measure because it almost gets lost in the noise,
> > but this seemed to help Dota 2 by a percent or two on my Broadwell
> > GT3e desktop.
> >
> > Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> > ---
> > src/intel/vulkan/genX_pipeline.c | 171 +++++++++++++++++++++++++++++++--------
> > 1 file changed, 137 insertions(+), 34 deletions(-)
> >
> > diff --git a/src/intel/vulkan/genX_pipeline.c b/src/intel/vulkan/genX_pipeline.c
> > index 71b9e30..d2af8b9 100644
> > --- a/src/intel/vulkan/genX_pipeline.c
> > +++ b/src/intel/vulkan/genX_pipeline.c
> > @@ -638,6 +638,133 @@ static const uint32_t vk_to_gen_stencil_op[] = {
> > [VK_STENCIL_OP_DECREMENT_AND_WRAP] = STENCILOP_DECR,
> > };
> >
> > +static bool
> > +may_write_stencil_face(const VkStencilOpState *face,
> > + VkCompareOp depthCompareOp)
> > +{
>
> This function triggers some false negatives. One example is
>
> face->compareOp == VK_COMPARE_OP_GREATER &&
> face->depthFailOp == VK_STENCIL_OP_KEEP &&
> face->passOp == VK_STENCIL_OP_KEEP &&
> face->failOp == VK_STENCIL_OP_INVERT &&
> depthCompareOp == don't care;
>
> This function returns false even though a stencil write occurs if the
> stencil test results in a fail.
Thanks for pointing out in the office that this actually isn't a false
negative. This function is correct, but I still think it could be
simplified. I really needed a visual to evaluate it as it currently is
written.
-Nanley
>
> The possible input combinations that affect writing to stencil can be
> divided up into 10 sets.
>
> s = stencil compare op
> d = depth compare op
> df = depth fail op
> sf = stencil fail op
> sp = stencil pass op
>
> s.Always | !s.Always
> d.Never | !d.Never | s.Never |
> | d.Always | | |
> !keep | | | |
> | | | |
> ------------|----------|------|--------------|--------------
> | | | |
> keep df.Keep | sp.Keep | | sf.Keep |
> | | | |
> | | | |
>
> We know that stencil won't be written if the function inputs land us in
> 3 of these sets (denoted by the *.Keep's above). I think this function
> would be easier to understand if it determined if we fell in one of the
> 3 instead of the 7. How about something like this:
>
> static bool
> wont_write_stencil_face(const VkStencilOpState *face,
> VkCompareOp depthCompareOp)
> {
> if (face->compareOp == VK_COMPARE_OP_NEVER &&
> face->failOp == VK_STENCIL_OP_KEEP)
> return true;
>
> if (face->compareOp == VK_COMPARE_OP_ALWAYS) {
> if (depthCompareOp == VK_COMPARE_OP_NEVER &&
> face->depthFailOp == VK_STENCIL_OP_KEEP)
> return true;
> if (depthCompareOp == VK_COMPARE_OP_ALWAYS &&
> face->passOp == VK_STENCIL_OP_KEEP)
> return true;
> }
> return false;
> }
>
> -Nanley
>
> > + /* If compareOp is ALWAYS then the stencil test will never fail and we can
> > + * ignore failOp. If it's not ALWAYS and failOp is not KEEP, we may write
> > + * stencil.
> > + */
> > + if (face->compareOp != VK_COMPARE_OP_ALWAYS &&
> > + face->failOp != VK_STENCIL_OP_KEEP)
> > + return true;
> > +
> > +
> > + /* If the compareOp is NEVER then the stencil test will never pass and the
> > + * passOp and depthFailOp don't matter. If compareOp isn't NEVER, then we
> > + * need to take them into account.
> > + */
> > + if (face->compareOp != VK_COMPARE_OP_NEVER) {
> > + /* If depthOp is NEVER then passOp doesn't matter. */
> > + if (depthCompareOp != VK_COMPARE_OP_NEVER &&
> > + face->passOp != VK_STENCIL_OP_KEEP)
> > + return true;
> > +
> > + /* If depthOp is ALWAYS then depthFailOp doesn't matter. */
> > + if (depthCompareOp != VK_COMPARE_OP_ALWAYS &&
> > + face->depthFailOp != VK_STENCIL_OP_KEEP)
> > + return true;
> > + }
> > +
> > + return false;
> > +}
> > +
> > +/* Intel hardware is fairly sensitive to whether or not depth/stencil writes
> > + * are enabled. In the presence of discards, it's fairly easy to get into the
> > + * non-promoted case which means a fairly big performance hit. From the Iron
> > + * Lake PRM, Vol 2, pt. 1, section 8.4.3.2, "Early Depth Test Cases":
> > + *
> > + * "Non-promoted depth (N) is active whenever the depth test can be done
> > + * early but it cannot determine whether or not to write source depth to
> > + * the depth buffer, therefore the depth write must be performed post pixel
> > + * shader. This includes cases where the pixel shader can kill pixels,
> > + * including via sampler chroma key, as well as cases where the alpha test
> > + * function is enabled, which kills pixels based on a programmable alpha
> > + * test. In this case, even if the depth test fails, the pixel cannot be
> > + * killed if a stencil write is indicated. Whether or not the stencil write
> > + * happens depends on whether or not the pixel is killed later. In these
> > + * cases if stencil test fails and stencil writes are off, the pixels can
> > + * also be killed early. If stencil writes are enabled, the pixels must be
> > + * treated as Computed depth (described above)."
> > + *
> > + * The same thing as mentioned in the stencil case can happen in the depth
> > + * case as well if it thinks it writes depth but, thanks to the depth test
> > + * being GL_EQUAL, the write doesn't actually matter. A little extra work
> > + * up-front to try and disable depth and stencil writes can make a big
> > + * difference.
> > + *
> > + * Unfortunately, the way depth and stencil testing is specified, there are
> > + * many case where, regardless of depth/stencil writes being enabled, nothing
> > + * actually gets written due to some other bit of state being set. This
> > + * function attempts to "sanitize" the depth stencil state and disable writes
> > + * and sometimes even testing whenever possible.
> > + */
> > +static void
> > +sanitize_ds_state(VkPipelineDepthStencilStateCreateInfo *state,
> > + bool *stencilWriteEnable,
> > + VkImageAspectFlags ds_aspects)
> > +{
> > + *stencilWriteEnable = state->stencilTestEnable;
> > +
> > + /* If the depth test is disabled, we won't be writing anything. */
> > + if (!state->depthTestEnable)
> > + state->depthWriteEnable = false;
> > +
> > + /* The Vulkan spec requires that if either depth or stencil is not present,
> > + * the pipeline is to act as if the test silently passes.
> > + */
> > + if (!(ds_aspects & VK_IMAGE_ASPECT_DEPTH_BIT)) {
> > + state->depthWriteEnable = false;
> > + state->depthCompareOp = VK_COMPARE_OP_ALWAYS;
> > + }
> > +
> > + if (!(ds_aspects & VK_IMAGE_ASPECT_STENCIL_BIT)) {
> > + *stencilWriteEnable = false;
> > + state->front.compareOp = VK_COMPARE_OP_ALWAYS;
> > + state->back.compareOp = VK_COMPARE_OP_ALWAYS;
> > + }
> > +
> > + /* If the stencil test is enabled and always fails, then we will never get
> > + * to the depth test so we can just disable the depth test entirely.
> > + */
> > + if (state->stencilTestEnable &&
> > + state->front.compareOp == VK_COMPARE_OP_NEVER &&
> > + state->back.compareOp == VK_COMPARE_OP_NEVER) {
> > + state->depthTestEnable = false;
> > + state->depthWriteEnable = false;
> > + }
> > +
> > + /* If depthCompareOp is EQUAL then the value we would be writing to the
> > + * depth buffer is the same as the value that's already there so there's no
> > + * point in writing it.
> > + */
> > + if (state->depthCompareOp == VK_COMPARE_OP_EQUAL)
> > + state->depthWriteEnable = false;
> > +
> > + /* If the stencil ops are such that we don't actually ever modify the
> > + * stencil buffer, we should disable writes.
> > + */
> > + if (!may_write_stencil_face(&state->front, state->depthCompareOp) &&
> > + !may_write_stencil_face(&state->back, state->depthCompareOp))
> > + *stencilWriteEnable = false;
> > +
> > + /* If the depth test always passes and we never write out depth, that's the
> > + * same as if the depth test is disabled entirely.
> > + */
> > + if (state->depthCompareOp == VK_COMPARE_OP_ALWAYS &&
> > + !state->depthWriteEnable)
> > + state->depthTestEnable = false;
> > +
> > + /* If the stencil test always passes and we never write out stencil, that's
> > + * the same as if the stencil test is disabled entirely.
> > + */
> > + if (state->front.compareOp == VK_COMPARE_OP_ALWAYS &&
> > + state->back.compareOp == VK_COMPARE_OP_ALWAYS &&
> > + !*stencilWriteEnable)
> > + state->stencilTestEnable = false;
> > +}
> > +
> > static void
> > emit_ds_state(struct anv_pipeline *pipeline,
> > const VkPipelineDepthStencilStateCreateInfo *pCreateInfo,
> > @@ -663,12 +790,20 @@ emit_ds_state(struct anv_pipeline *pipeline,
> > return;
> > }
> >
> > + VkImageAspectFlags ds_aspects = 0;
> > + if (subpass->depth_stencil_attachment != VK_ATTACHMENT_UNUSED) {
> > + VkFormat depth_stencil_format =
> > + pass->attachments[subpass->depth_stencil_attachment].format;
> > + ds_aspects = vk_format_aspects(depth_stencil_format);
> > + }
> > +
> > VkPipelineDepthStencilStateCreateInfo info = *pCreateInfo;
> > + sanitize_ds_state(&info, &pipeline->writes_stencil, ds_aspects);
> > + pipeline->writes_depth = info.depthWriteEnable;
> > + pipeline->depth_test_enable = info.depthTestEnable;
> >
> > /* VkBool32 depthBoundsTestEnable; // optional (depth_bounds_test) */
> >
> > - pipeline->writes_stencil = info.stencilTestEnable;
> > -
> > #if GEN_GEN <= 7
> > struct GENX(DEPTH_STENCIL_STATE) depth_stencil = {
> > #else
> > @@ -690,38 +825,6 @@ emit_ds_state(struct anv_pipeline *pipeline,
> > .BackfaceStencilTestFunction = vk_to_gen_compare_op[info.back.compareOp],
> > };
> >
> > - VkImageAspectFlags aspects = 0;
> > - if (subpass->depth_stencil_attachment != VK_ATTACHMENT_UNUSED) {
> > - VkFormat depth_stencil_format =
> > - pass->attachments[subpass->depth_stencil_attachment].format;
> > - aspects = vk_format_aspects(depth_stencil_format);
> > - }
> > -
> > - /* The Vulkan spec requires that if either depth or stencil is not present,
> > - * the pipeline is to act as if the test silently passes.
> > - */
> > - if (!(aspects & VK_IMAGE_ASPECT_DEPTH_BIT)) {
> > - depth_stencil.DepthBufferWriteEnable = false;
> > - depth_stencil.DepthTestFunction = PREFILTEROPALWAYS;
> > - }
> > -
> > - if (!(aspects & VK_IMAGE_ASPECT_STENCIL_BIT)) {
> > - pipeline->writes_stencil = false;
> > - depth_stencil.StencilTestFunction = PREFILTEROPALWAYS;
> > - depth_stencil.BackfaceStencilTestFunction = PREFILTEROPALWAYS;
> > - }
> > -
> > - /* From the Broadwell PRM:
> > - *
> > - * "If Depth_Test_Enable = 1 AND Depth_Test_func = EQUAL, the
> > - * Depth_Write_Enable must be set to 0."
> > - */
> > - if (info.depthTestEnable && info.depthCompareOp == VK_COMPARE_OP_EQUAL)
> > - depth_stencil.DepthBufferWriteEnable = false;
> > -
> > - pipeline->writes_depth = depth_stencil.DepthBufferWriteEnable;
> > - pipeline->depth_test_enable = depth_stencil.DepthTestEnable;
> > -
> > #if GEN_GEN <= 7
> > GENX(DEPTH_STENCIL_STATE_pack)(NULL, depth_stencil_dw, &depth_stencil);
> > #else
> > --
> > 2.5.0.400.gff86faf
> >
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
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