[FFmpeg-devel] [PATCH] vulkan: use a single command buffer per command buffer pool

[FFmpeg-devel] [PATCH] vulkan: use a single command buffer per command buffer pool

[Lynne]

We violated the spec, which, despite the actual command buffer pool
*not* being involved in any functions which require external synchronization
of the pool, *require* external synchronization even if only the
command buffers are used.

This also has the effect of *significantly* speeding up execution
in case command buffers are contended.
---
 libavutil/hwcontext_vulkan.c |  1 -
 libavutil/vulkan.c           | 78 +++++++++++++++++++++---------------
 libavutil/vulkan.h           |  2 +-
 3 files changed, 47 insertions(+), 34 deletions(-)

diff --git a/libavutil/hwcontext_vulkan.c b/libavutil/hwcontext_vulkan.c
index 32203b2f06..d7822d4629 100644
--- a/libavutil/hwcontext_vulkan.c
+++ b/libavutil/hwcontext_vulkan.c
@@ -673,7 +673,6 @@ static VkBool32 VKAPI_CALL vk_dbg_callback(VkDebugUtilsMessageSeverityFlagBitsEX
     case 0xfd92477a: /* BestPractices-vkAllocateMemory-small-allocation */
     case 0x618ab1e7: /* VUID-VkImageViewCreateInfo-usage-02275 */
     case 0x30f4ac70: /* VUID-VkImageCreateInfo-pNext-06811 */
-    case 0xa05b236e: /* UNASSIGNED-Threading-MultipleThreads-Write */
         return VK_FALSE;
     default:
         break;
diff --git a/libavutil/vulkan.c b/libavutil/vulkan.c
index d880d52272..8f444b2dfe 100644
--- a/libavutil/vulkan.c
+++ b/libavutil/vulkan.c
@@ -280,15 +280,19 @@ void ff_vk_exec_pool_free(FFVulkanContext *s, FFVkExecPool *pool)
         av_freep(&sd->desc_sets);
     }
 
-    if (pool->cmd_bufs)
-        vk->FreeCommandBuffers(s->hwctx->act_dev, pool->cmd_buf_pool,
-                               pool->pool_size, pool->cmd_bufs);
-    if (pool->cmd_buf_pool)
-        vk->DestroyCommandPool(s->hwctx->act_dev, pool->cmd_buf_pool, s->hwctx->alloc);
+    for (int i = 0; i < pool->pool_size; i++) {
+        if (pool->cmd_buf_pools[i])
+            vk->FreeCommandBuffers(s->hwctx->act_dev, pool->cmd_buf_pools[i],
+                                   1, &pool->cmd_bufs[i]);
+
+        if (pool->cmd_buf_pools[i])
+            vk->DestroyCommandPool(s->hwctx->act_dev, pool->cmd_buf_pools[i], s->hwctx->alloc);
+    }
     if (pool->query_pool)
         vk->DestroyQueryPool(s->hwctx->act_dev, pool->query_pool, s->hwctx->alloc);
 
     av_free(pool->query_data);
+    av_free(pool->cmd_buf_pools);
     av_free(pool->cmd_bufs);
     av_free(pool->contexts);
 }
@@ -316,19 +320,10 @@ int ff_vk_exec_pool_init(FFVulkanContext *s, AVVulkanDeviceQueueFamily *qf,
             return AVERROR(EINVAL);
     }
 
-    /* Create command pool */
-    cqueue_create = (VkCommandPoolCreateInfo) {
-        .sType              = VK_STRUCTURE_TYPE_COMMAND_POOL_CREATE_INFO,
-        .flags              = VK_COMMAND_POOL_CREATE_TRANSIENT_BIT |
-                              VK_COMMAND_POOL_CREATE_RESET_COMMAND_BUFFER_BIT,
-        .queueFamilyIndex   = qf->idx,
-    };
-    ret = vk->CreateCommandPool(s->hwctx->act_dev, &cqueue_create,
-                                s->hwctx->alloc, &pool->cmd_buf_pool);
-    if (ret != VK_SUCCESS) {
-        av_log(s, AV_LOG_ERROR, "Command pool creation failure: %s\n",
-               ff_vk_ret2str(ret));
-        err = AVERROR_EXTERNAL;
+    /* Allocate space for command buffer pools */
+    pool->cmd_buf_pools = av_malloc(nb_contexts*sizeof(*pool->cmd_buf_pools));
+    if (!pool->cmd_buf_pools) {
+        err = AVERROR(ENOMEM);
         goto fail;
     }
 
@@ -339,20 +334,39 @@ int ff_vk_exec_pool_init(FFVulkanContext *s, AVVulkanDeviceQueueFamily *qf,
         goto fail;
     }
 
-    /* Allocate command buffer */
-    cbuf_create = (VkCommandBufferAllocateInfo) {
-        .sType              = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO,
-        .level              = VK_COMMAND_BUFFER_LEVEL_PRIMARY,
-        .commandPool        = pool->cmd_buf_pool,
-        .commandBufferCount = nb_contexts,
-    };
-    ret = vk->AllocateCommandBuffers(s->hwctx->act_dev, &cbuf_create,
-                                     pool->cmd_bufs);
-    if (ret != VK_SUCCESS) {
-        av_log(s, AV_LOG_ERROR, "Command buffer alloc failure: %s\n",
-               ff_vk_ret2str(ret));
-        err = AVERROR_EXTERNAL;
-        goto fail;
+    for (int i = 0; i < nb_contexts; i++) {
+        /* Create command pool */
+        cqueue_create = (VkCommandPoolCreateInfo) {
+            .sType              = VK_STRUCTURE_TYPE_COMMAND_POOL_CREATE_INFO,
+            .flags              = VK_COMMAND_POOL_CREATE_TRANSIENT_BIT |
+                                  VK_COMMAND_POOL_CREATE_RESET_COMMAND_BUFFER_BIT,
+            .queueFamilyIndex   = qf->idx,
+        };
+
+        ret = vk->CreateCommandPool(s->hwctx->act_dev, &cqueue_create,
+                                    s->hwctx->alloc, &pool->cmd_buf_pools[i]);
+        if (ret != VK_SUCCESS) {
+            av_log(s, AV_LOG_ERROR, "Command pool creation failure: %s\n",
+                   ff_vk_ret2str(ret));
+            err = AVERROR_EXTERNAL;
+            goto fail;
+        }
+
+        /* Allocate command buffer */
+        cbuf_create = (VkCommandBufferAllocateInfo) {
+            .sType              = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO,
+            .level              = VK_COMMAND_BUFFER_LEVEL_PRIMARY,
+            .commandPool        = pool->cmd_buf_pools[i],
+            .commandBufferCount = 1,
+        };
+        ret = vk->AllocateCommandBuffers(s->hwctx->act_dev, &cbuf_create,
+                                         &pool->cmd_bufs[i]);
+        if (ret != VK_SUCCESS) {
+            av_log(s, AV_LOG_ERROR, "Command buffer alloc failure: %s\n",
+                   ff_vk_ret2str(ret));
+            err = AVERROR_EXTERNAL;
+            goto fail;
+        }
     }
 
     /* Query pool */
diff --git a/libavutil/vulkan.h b/libavutil/vulkan.h
index 4ea68e3ecc..2fb7f7c2de 100644
--- a/libavutil/vulkan.h
+++ b/libavutil/vulkan.h
@@ -253,7 +253,7 @@ typedef struct FFVkExecPool {
     FFVkExecContext *contexts;
     atomic_uint_least64_t idx;
 
-    VkCommandPool cmd_buf_pool;
+    VkCommandPool *cmd_buf_pools;
     VkCommandBuffer *cmd_bufs;
     int pool_size;
 
-- 
2.47.2
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Re: [FFmpeg-devel] [PATCH] vulkan: use a single command buffer per command buffer pool

[Jerome Martinez]

Le 16/04/2025 à 15:26, Lynne a écrit :
> We violated the spec, which, despite the actual command buffer pool
> *not* being involved in any functions which require external synchronization
> of the pool, *require* external synchronization even if only the
> command buffers are used.
>
> This also has the effect of *significantly* speeding up execution
> in case command buffers are contended.

I can confirm a +6% on 16-bit content on a RTX 4070 Ti.
With a 2K 16-slice content:
- It was freezing after ~300 frames on a RTX 4070 Ti, now it runs slowly 
but smoothly,
- The UI was frozen on a RTX 3050, still some kind of freeze with this 
patch but it is better (especially with -thread 1)

no regression found.
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