src/daedalus_core.c

@@ -325,8 +325,8 @@ static int dispatch_idct8_qpu(daedalus_ctx *ctx,
         ._pad = 0,
     };
 
-    VkCommandBuffer cb = v3d_runner_alloc_cmdbuf(ctx->runner);
+    if (v3d_runner_pipeline_cmdbuf_reset(ctx->runner, &ctx->idct8_pipe)) goto fail;
-    if (cb == VK_NULL_HANDLE) goto fail;
+    VkCommandBuffer cb = ctx->idct8_pipe.cb;
     VkCommandBufferBeginInfo cbbi = { .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO };
     vkBeginCommandBuffer(cb, &cbbi);
     vkCmdBindPipeline(cb, VK_PIPELINE_BIND_POINT_COMPUTE,
@@ -442,8 +442,8 @@ static int dispatch_lpf_qpu(daedalus_ctx *ctx, int wd_8,
     if (v3d_runner_bind_buffers(ctx->runner, p, binds, 2)) goto fail;
 
     uint32_t wg_count = (uint32_t)((n_edges + 31) / 32);
-    VkCommandBuffer cb = v3d_runner_alloc_cmdbuf(ctx->runner);
+    if (v3d_runner_pipeline_cmdbuf_reset(ctx->runner, p)) goto fail;
-    if (cb == VK_NULL_HANDLE) goto fail;
+    VkCommandBuffer cb = p->cb;
     VkCommandBufferBeginInfo cbbi = { .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO };
     vkBeginCommandBuffer(cb, &cbbi);
     vkCmdBindPipeline(cb, VK_PIPELINE_BIND_POINT_COMPUTE, p->pipeline);
@@ -530,8 +530,8 @@ static int dispatch_mc_8h_qpu(daedalus_ctx *ctx,
     mc_pc pc = { .n_blocks = (uint32_t) n_blocks,
                  .dst_stride_u8 = (uint32_t) dst_stride,
                  .src_stride_u8 = (uint32_t) src_stride };
-    VkCommandBuffer cb = v3d_runner_alloc_cmdbuf(ctx->runner);
+    if (v3d_runner_pipeline_cmdbuf_reset(ctx->runner, &ctx->mc8h_pipe)) goto fail;
-    if (cb == VK_NULL_HANDLE) goto fail;
+    VkCommandBuffer cb = ctx->mc8h_pipe.cb;
     VkCommandBufferBeginInfo cbbi = { .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO };
     vkBeginCommandBuffer(cb, &cbbi);
     vkCmdBindPipeline(cb, VK_PIPELINE_BIND_POINT_COMPUTE, ctx->mc8h_pipe.pipeline);
@@ -615,8 +615,8 @@ static int dispatch_cdef_qpu(daedalus_ctx *ctx,
     cdef_pc pc = { .n_blocks = (uint32_t) n_blocks,
                    .tmp_stride_u16 = 16,
                    .dst_stride_u8 = (uint32_t) dst_stride };
-    VkCommandBuffer cb = v3d_runner_alloc_cmdbuf(ctx->runner);
+    if (v3d_runner_pipeline_cmdbuf_reset(ctx->runner, &ctx->cdef_pipe)) goto fail;
-    if (cb == VK_NULL_HANDLE) goto fail;
+    VkCommandBuffer cb = ctx->cdef_pipe.cb;
     VkCommandBufferBeginInfo cbbi = { .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO };
     vkBeginCommandBuffer(cb, &cbbi);
     vkCmdBindPipeline(cb, VK_PIPELINE_BIND_POINT_COMPUTE, ctx->cdef_pipe.pipeline);
@@ -691,8 +691,8 @@ static int dispatch_h264_deblock_qpu(daedalus_ctx *ctx,
     uint32_t wg_count = (uint32_t)((n_edges + 15) / 16);
     h264deblock_pc pc = { .n_edges = (uint32_t) n_edges,
                           .dst_stride_u8 = (uint32_t) dst_stride };
-    VkCommandBuffer cb = v3d_runner_alloc_cmdbuf(ctx->runner);
+    if (v3d_runner_pipeline_cmdbuf_reset(ctx->runner, &ctx->h264deblock_pipe)) goto fail;
-    if (cb == VK_NULL_HANDLE) goto fail;
+    VkCommandBuffer cb = ctx->h264deblock_pipe.cb;
     VkCommandBufferBeginInfo cbbi = { .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO };
     vkBeginCommandBuffer(cb, &cbbi);
     vkCmdBindPipeline(cb, VK_PIPELINE_BIND_POINT_COMPUTE, ctx->h264deblock_pipe.pipeline);

src/v3d_runner.c

@@ -486,12 +486,27 @@ int v3d_runner_create_pipeline(v3d_runner *r, const char *spv_path,
         .pSetLayouts = &out->ds_layout,
     };
     CHK(vkAllocateDescriptorSets(r->device, &dsai, &out->desc_set));
+
+    /* Persistent command buffer — pool was created with
+     * RESET_COMMAND_BUFFER_BIT (see v3d_runner_create) so dispatch
+     * sites can call vkResetCommandBuffer on this same cb instead
+     * of paying vkAllocateCommandBuffers per call. */
+    VkCommandBufferAllocateInfo cbai = {
+        .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO,
+        .commandPool = r->pool,
+        .level = VK_COMMAND_BUFFER_LEVEL_PRIMARY,
+        .commandBufferCount = 1,
+    };
+    CHK(vkAllocateCommandBuffers(r->device, &cbai, &out->cb));
+
     return 0;
 }
 
 void v3d_runner_destroy_pipeline(v3d_runner *r, v3d_pipeline *p)
 {
     if (!p || p->pipeline == VK_NULL_HANDLE) return;
+    if (p->cb != VK_NULL_HANDLE)
+        vkFreeCommandBuffers(r->device, r->pool, 1, &p->cb);
     vkDestroyPipeline(r->device, p->pipeline, NULL);
     vkDestroyPipelineLayout(r->device, p->layout, NULL);
     vkDestroyDescriptorPool(r->device, p->pool, NULL);  /* frees its set */
@@ -499,6 +514,13 @@ void v3d_runner_destroy_pipeline(v3d_runner *r, v3d_pipeline *p)
     memset(p, 0, sizeof(*p));
 }
 
+int v3d_runner_pipeline_cmdbuf_reset(v3d_runner *r, v3d_pipeline *p)
+{
+    (void) r;
+    if (!p || p->cb == VK_NULL_HANDLE) return -1;
+    return vkResetCommandBuffer(p->cb, 0) == VK_SUCCESS ? 0 : -1;
+}
+
 int v3d_runner_bind_buffers(v3d_runner *r, v3d_pipeline *p,
                             const v3d_buffer *bufs, uint32_t n)
 {

src/v3d_runner.h

@@ -34,6 +34,12 @@ typedef struct {
     VkDescriptorSet        desc_set;
     uint32_t               n_ssbos;
     uint32_t               push_const_size;
+    /* Persistent command buffer.  Allocated at create-pipeline time;
+     * dispatch sites use v3d_runner_pipeline_cmdbuf_reset() to
+     * vkResetCommandBuffer instead of paying vkAllocateCommandBuffers
+     * per dispatch.  Pool flagged RESET_COMMAND_BUFFER_BIT so reset
+     * is permitted. */
+    VkCommandBuffer        cb;
 } v3d_pipeline;
 
 /*
@@ -121,6 +127,12 @@ int  v3d_runner_bind_buffers(v3d_runner   *r,
 /* Allocate a primary command buffer from the runner's pool. */
 VkCommandBuffer v3d_runner_alloc_cmdbuf(v3d_runner *r);
 
+/* Reset @p->cb so it can be re-recorded.  Returns 0 on success.
+ * Replaces v3d_runner_alloc_cmdbuf() on the dispatch hot path —
+ * vkResetCommandBuffer is O(1) vs vkAllocateCommandBuffers' ~1-5us
+ * driver cost. */
+int v3d_runner_pipeline_cmdbuf_reset(v3d_runner *r, v3d_pipeline *p);
+
 /* Submit `cb` to the queue and wait for completion. The classic
  * timed operation. Returns 0 on success.
  */