9.6. Pipeline Cache

Pipeline cache objects allow the result of pipeline construction to be reused between pipelines and between runs of an application. Reuse between pipelines is achieved by passing the same pipeline cache object when creating multiple related pipelines. Reuse across runs of an application is achieved by retrieving pipeline cache contents in one run of an application, saving the contents, and using them to preinitialize a pipeline cache on a subsequent run. The contents of the pipeline cache objects are managed by the implementation. Applications can manage the host memory consumed by a pipeline cache object and control the amount of data retrieved from a pipeline cache object.

Pipeline cache objects are created by calling:

 

VkResult vkCreatePipelineCache(
    VkDevice                                    device,
    const VkPipelineCacheCreateInfo*            pCreateInfo,
    const VkAllocationCallbacks*                pAllocator,
    VkPipelineCache*                            pPipelineCache);

[Note]Note

Applications can track and manage the total host memory size of a pipeline cache object using the pAllocator. Applications can limit the amount of data retrieved from a pipeline cache object in vkGetPipeineCacheData. Implementations should not internally limit the total number of entries added to a pipeline cache object or the total host memory consumed.

The VkPipelineCacheCreateInfo structure is defined as:

 

typedef struct VkPipelineCacheCreateInfo {
    VkStructureType               sType;
    const void*                   pNext;
    VkPipelineCacheCreateFlags    flags;
    size_t                        initialDataSize;
    const void*                   pInitialData;
} VkPipelineCacheCreateInfo;

Once created, a pipeline cache can be passed to the vkCreateGraphicsPipelines and vkCreateComputePipelines commands. If the pipeline cache passed into these commands is not VK_NULL_HANDLE, the implementation will query it for possible reuse opportunities and update it with new content. The use of the pipeline cache object in these commands is internally synchronized, and the same pipeline cache object can be used in multiple threads simultaneously.

[Note]Note

Implementations should make every effort to limit any critical sections to the actual accesses to the cache, which is expected to be significantly shorter than the duration of the vkCreateGraphicsPipelines and vkCreateComputePipelines commands.

Pipeline cache objects can be merged using the command:

 

VkResult vkMergePipelineCaches(
    VkDevice                                    device,
    VkPipelineCache                             dstCache,
    uint32_t                                    srcCacheCount,
    const VkPipelineCache*                      pSrcCaches);

[Note]Note

The details of the merge operation are implementation dependent, but implementations should merge the contents of the specified pipelines and prune duplicate entries.

Data can be retrieved from a pipeline cache object using the command:

 

VkResult vkGetPipelineCacheData(
    VkDevice                                    device,
    VkPipelineCache                             pipelineCache,
    size_t*                                     pDataSize,
    void*                                       pData);

If pData is NULL, then the maximum size of the data that can be retrieved from the pipeline cache, in bytes, is returned in pDataSize. Otherwise, pDataSize must point to a variable set by the user to the size of the buffer, in bytes, pointed to by pData, and on return the variable is overwritten with the amount of data actually written to pData.

If dataSize is less than the maximum size that can be retrieved by the pipeline cache, at most pDataSize bytes will be written to pData, and vkGetPipelineCacheData will return VK_INCOMPLETE. Any data written to pData is valid and can be provided as the pInitialData member of the VkPipelineCacheCreateInfo structure passed to vkCreatePipelineCache.

Applications can store the data retrieved from the pipeline cache, and use these data, possibly in a future run of the application, to populate new pipeline cache objects. The results of pipeline compiles, however, may depend on the vendor ID, device ID, driver version, and other details of the device. To enable applications to detect when previously retrieved data is incompatible with the device, the initial bytes written to pData must be a header consisting of the following members:

Table 9.1. Layout for pipeline cache header version VK_PIPELINE_CACHE_HEADER_VERSION_ONE

Offset Size Meaning

0

4

length in bytes of the entire pipeline cache header written as a stream of bytes, with the least significant byte first

4

4

a VkPipelineCacheHeaderVersion value written as a stream of bytes, with the least significant byte first

8

4

a vendor ID equal to VkPhysicalDeviceProperties::vendorID written as a stream of bytes, with the least significant byte first

12

4

a device ID equal to VkPhysicalDeviceProperties::deviceID written as a stream of bytes, with the least significant byte first

16

VK_UUID_SIZE

a pipeline cache ID equal to VkPhysicalDeviceProperties::pipelineCacheUUID


The first four bytes encode the length of the entire pipeline header, in bytes. This value includes all fields in the header including the pipeline cache version field and the size of the length field.

The next four bytes encode the pipeline cache version. This field is interpreted as a VkPipelineCacheHeaderVersion value, and must have one of the following values:

 

typedef enum VkPipelineCacheHeaderVersion {
    VK_PIPELINE_CACHE_HEADER_VERSION_ONE = 1,
} VkPipelineCacheHeaderVersion;

A consumer of the pipeline cache should use the cache version to interpret the remainder of the cache header.

If dataSize is less than what is necessary to store this header, nothing will be written to pData and zero will be written to dataSize.

To destroy a pipeline cache, call:

 

void vkDestroyPipelineCache(
    VkDevice                                    device,
    VkPipelineCache                             pipelineCache,
    const VkAllocationCallbacks*                pAllocator);