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vulkan: Optimize implicit begin_subpass barrier

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Rather than adding an implicit barrier on the first subpass
unconditionally, track in what subpasses attachments are used for the
first time and only add dependencies if none exist and there might be an
image transition.

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36985>
This commit is contained in:
Lars-Ivar Hesselberg Simonsen 2025-08-25 15:22:24 +02:00 • committed by Marge Bot
parent c0def2cf27
commit eccc198284
1 changed files with 54 additions and 53 deletions
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107
src/vulkan/runtime/vk_render_pass.c
View file

@ -1652,7 +1652,7 @@ transition_view_mask(struct vk_command_buffer *cmd_buffer,
return transition_view_mask;
}
static void
static uint32_t
transition_attachment(struct vk_command_buffer *cmd_buffer,
uint32_t att_idx,
uint32_t view_mask,
@ -1726,6 +1726,8 @@ transition_attachment(struct vk_command_buffer *cmd_buffer,
att_view_state->layout = layout;
att_view_state->stencil_layout = stencil_layout;
}
return view_mask;
}
static void
@ -2131,6 +2133,7 @@ begin_subpass(struct vk_command_buffer *cmd_buffer,
* implicit one. */
STACK_ARRAY(VkMemoryBarrier2, mem_barriers, pass->dependency_count + 1);
uint32_t mem_barrier_count = 0;
bool external_dependency = false;
for (uint32_t d = 0; d < pass->dependency_count; d++) {
const struct vk_subpass_dependency *dep = &pass->dependencies[d];
if (dep->dst_subpass != subpass_idx)
@ -2178,9 +2181,58 @@ begin_subpass(struct vk_command_buffer *cmd_buffer,
.dstStageMask = dep->dst_stage_mask,
.dstAccessMask = dep->dst_access_mask,
};
external_dependency |= (dep->src_subpass == VK_SUBPASS_EXTERNAL);
}
if (subpass_idx == 0) {
uint32_t max_image_barrier_count = 0;
for (uint32_t a = 0; a < subpass->attachment_count; a++) {
const struct vk_subpass_attachment *sp_att = &subpass->attachments[a];
if (sp_att->attachment == VK_ATTACHMENT_UNUSED)
continue;
assert(sp_att->attachment < pass->attachment_count);
const struct vk_render_pass_attachment *rp_att =
&pass->attachments[sp_att->attachment];
max_image_barrier_count += util_bitcount(subpass->view_mask) *
util_bitcount(rp_att->aspects);
}
if (pass->fragment_density_map.attachment != VK_ATTACHMENT_UNUSED)
max_image_barrier_count += util_bitcount(subpass->view_mask);
STACK_ARRAY(VkImageMemoryBarrier2, image_barriers, max_image_barrier_count);
uint32_t image_barrier_count = 0;
bool has_layout_transition = false;
for (uint32_t a = 0; a < subpass->attachment_count; a++) {
const struct vk_subpass_attachment *sp_att = &subpass->attachments[a];
if (sp_att->attachment == VK_ATTACHMENT_UNUSED)
continue;
/* If we're using an initial layout, the attachment will already be
* marked as transitioned and this will be a no-op.
*/
uint32_t transitioned_views =
transition_attachment(cmd_buffer, sp_att->attachment,
subpass->view_mask,
sp_att->layout, sp_att->stencil_layout,
&image_barrier_count,
max_image_barrier_count,
image_barriers);
has_layout_transition |= (sp_att->first_subpass & transitioned_views) != 0;
}
if (pass->fragment_density_map.attachment != VK_ATTACHMENT_UNUSED) {
transition_attachment(cmd_buffer, pass->fragment_density_map.attachment,
subpass->view_mask,
pass->fragment_density_map.layout,
VK_IMAGE_LAYOUT_UNDEFINED,
&image_barrier_count,
max_image_barrier_count,
image_barriers);
}
assert(image_barrier_count <= max_image_barrier_count);
if (has_layout_transition && !external_dependency) {
/* From the Vulkan 1.3.232 spec:
*
* "If there is no subpass dependency from VK_SUBPASS_EXTERNAL to the
@ -2204,13 +2256,6 @@ begin_subpass(struct vk_command_buffer *cmd_buffer,
* VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT;
* .dependencyFlags = 0;
* };"
*
* We could track individual subpasses and attachments and views to make
* sure we only insert this barrier when it's absolutely necessary.
* However, this is only going to happen for the first subpass and
* you're probably going to take a stall in BeginRenderPass() anyway.
* If this is ever a perf problem, we can re-evaluate and do something
* more intellegent at that time.
*/
mem_barriers[mem_barrier_count++] = (VkMemoryBarrier2){
.sType = VK_STRUCTURE_TYPE_MEMORY_BARRIER_2,
@ -2225,50 +2270,6 @@ begin_subpass(struct vk_command_buffer *cmd_buffer,
};
}
uint32_t max_image_barrier_count = 0;
for (uint32_t a = 0; a < subpass->attachment_count; a++) {
const struct vk_subpass_attachment *sp_att = &subpass->attachments[a];
if (sp_att->attachment == VK_ATTACHMENT_UNUSED)
continue;
assert(sp_att->attachment < pass->attachment_count);
const struct vk_render_pass_attachment *rp_att =
&pass->attachments[sp_att->attachment];
max_image_barrier_count += util_bitcount(subpass->view_mask) *
util_bitcount(rp_att->aspects);
}
if (pass->fragment_density_map.attachment != VK_ATTACHMENT_UNUSED)
max_image_barrier_count += util_bitcount(subpass->view_mask);
STACK_ARRAY(VkImageMemoryBarrier2, image_barriers, max_image_barrier_count);
uint32_t image_barrier_count = 0;
for (uint32_t a = 0; a < subpass->attachment_count; a++) {
const struct vk_subpass_attachment *sp_att = &subpass->attachments[a];
if (sp_att->attachment == VK_ATTACHMENT_UNUSED)
continue;
/* If we're using an initial layout, the attachment will already be
* marked as transitioned and this will be a no-op.
*/
transition_attachment(cmd_buffer, sp_att->attachment,
subpass->view_mask,
sp_att->layout, sp_att->stencil_layout,
&image_barrier_count,
max_image_barrier_count,
image_barriers);
}
if (pass->fragment_density_map.attachment != VK_ATTACHMENT_UNUSED) {
transition_attachment(cmd_buffer, pass->fragment_density_map.attachment,
subpass->view_mask,
pass->fragment_density_map.layout,
VK_IMAGE_LAYOUT_UNDEFINED,
&image_barrier_count,
max_image_barrier_count,
image_barriers);
}
assert(image_barrier_count <= max_image_barrier_count);
if (mem_barrier_count > 0 || image_barrier_count > 0) {
const VkDependencyInfo dependency_info = {
.sType = VK_STRUCTURE_TYPE_DEPENDENCY_INFO,