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vulkan: Optimize implicit end_subpass barrier

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Rather than adding an implicit barrier on the last subpass
unconditionally, track in what subpasses attachments are used for the
last 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 2025-08-26 13:37:12 +02:00 • committed by Marge Bot
parent eccc198284
commit e6dae6ef5f
1 changed files with 32 additions and 16 deletions
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48
src/vulkan/runtime/vk_render_pass.c
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@ -2428,6 +2428,8 @@ end_subpass(struct vk_command_buffer *cmd_buffer,
{
const struct vk_render_pass *pass = cmd_buffer->render_pass;
const uint32_t subpass_idx = cmd_buffer->subpass_idx;
assert(subpass_idx < pass->subpass_count);
const struct vk_subpass *subpass = &pass->subpasses[subpass_idx];
struct vk_device_dispatch_table *disp =
&cmd_buffer->base.device->dispatch_table;
@ -2454,7 +2456,26 @@ end_subpass(struct vk_command_buffer *cmd_buffer,
};
}
if (subpass_idx == pass->subpass_count - 1) {
/* If we have a barrier, we have an external dependency */
bool external_dependency = mem_barrier_count > 0;
if (!external_dependency) {
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;
const struct vk_render_pass_attachment *rp_att =
&pass->attachments[sp_att->attachment];
uint32_t view_mask = transition_view_mask(cmd_buffer, sp_att->attachment,
subpass->view_mask,
rp_att->final_layout,
rp_att->final_stencil_layout);
has_layout_transition |= (sp_att->last_subpass & view_mask) != 0;
}
/* From the Vulkan 1.3.232 spec:
*
* "Similarly, if there is no subpass dependency from the last
@ -2475,22 +2496,17 @@ end_subpass(struct vk_command_buffer *cmd_buffer,
* .dstAccessMask = 0;
* .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 last subpass and
* you're probably going to take a stall in EndRenderPass() 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,
.srcStageMask = VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT,
.srcAccessMask = VK_ACCESS_2_COLOR_ATTACHMENT_WRITE_BIT |
VK_ACCESS_2_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT,
.dstStageMask = VK_PIPELINE_STAGE_2_NONE,
.dstAccessMask = VK_ACCESS_2_NONE,
};
if (has_layout_transition) {
mem_barriers[mem_barrier_count++] = (VkMemoryBarrier2){
.sType = VK_STRUCTURE_TYPE_MEMORY_BARRIER_2,
.srcStageMask = VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT,
.srcAccessMask = VK_ACCESS_2_COLOR_ATTACHMENT_WRITE_BIT |
VK_ACCESS_2_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT,
.dstStageMask = VK_PIPELINE_STAGE_2_NONE,
.dstAccessMask = VK_ACCESS_2_NONE,
};
}
}
if (mem_barrier_count > 0) {