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// Copyright (c) 2015-2018 Khronos Group. This work is licensed under a
// Creative Commons Attribution 4.0 International License; see
// http://creativecommons.org/licenses/by/4.0/
[[queries]]
= Queries
_Queries_ provide a mechanism to return information about the processing of
a sequence of Vulkan commands.
Query operations are asynchronous, and as such, their results are not
returned immediately.
Instead, their results, and their availability status, are stored in a
<<queries-pools, Query Pool>>.
The state of these queries can: be read back on the host, or copied to a
buffer object on the device.
The supported query types are <<queries-occlusion,Occlusion Queries>>,
<<queries-pipestats,Pipeline Statistics Queries>>, and <<queries-timestamps,
Timestamp Queries>>.
[[queries-pools]]
== Query Pools
[open,refpage='VkQueryPool',desc='Opaque handle to a query pool object',type='handles']
--
Queries are managed using _query pool_ objects.
Each query pool is a collection of a specific number of queries of a
particular type.
Query pools are represented by sname:VkQueryPool handles:
include::../api/handles/VkQueryPool.txt[]
--
[open,refpage='vkCreateQueryPool',desc='Create a new query pool object',type='protos']
--
To create a query pool, call:
include::../api/protos/vkCreateQueryPool.txt[]
* pname:device is the logical device that creates the query pool.
* pname:pCreateInfo is a pointer to an instance of the
sname:VkQueryPoolCreateInfo structure containing the number and type of
queries to be managed by the pool.
* pname:pAllocator controls host memory allocation as described in the
<<memory-allocation, Memory Allocation>> chapter.
* pname:pQueryPool is a pointer to a slink:VkQueryPool handle in which the
resulting query pool object is returned.
include::../validity/protos/vkCreateQueryPool.txt[]
--
[open,refpage='VkQueryPoolCreateInfo',desc='Structure specifying parameters of a newly created query pool',type='structs']
--
The sname:VkQueryPoolCreateInfo structure is defined as:
include::../api/structs/VkQueryPoolCreateInfo.txt[]
* pname:sType is the type of this structure.
* pname:pNext is `NULL` or a pointer to an extension-specific structure.
* pname:flags is reserved for future use.
* pname:queryType is a elink:VkQueryType value specifying the type of
queries managed by the pool.
* pname:queryCount is the number of queries managed by the pool.
* pname:pipelineStatistics is a bitmask of
elink:VkQueryPipelineStatisticFlagBits specifying which counters will be
returned in queries on the new pool, as described below in
<<queries-pipestats>>.
pname:pipelineStatistics is ignored if pname:queryType is not
ename:VK_QUERY_TYPE_PIPELINE_STATISTICS.
.Valid Usage
****
* [[VUID-VkQueryPoolCreateInfo-queryType-00791]]
If the <<features-features-pipelineStatisticsQuery,pipeline statistics
queries>> feature is not enabled, pname:queryType must: not be
ename:VK_QUERY_TYPE_PIPELINE_STATISTICS
* [[VUID-VkQueryPoolCreateInfo-queryType-00792]]
If pname:queryType is ename:VK_QUERY_TYPE_PIPELINE_STATISTICS,
pname:pipelineStatistics must: be a valid combination of
elink:VkQueryPipelineStatisticFlagBits values
****
include::../validity/structs/VkQueryPoolCreateInfo.txt[]
--
[open,refpage='VkQueryPoolCreateFlags',desc='Reserved for future use',type='enums']
--
include::../api/flags/VkQueryPoolCreateFlags.txt[]
sname:VkQueryPoolCreateFlags is a bitmask type for setting a mask, but is
currently reserved for future use.
--
[open,refpage='vkDestroyQueryPool',desc='Destroy a query pool object',type='protos']
--
To destroy a query pool, call:
include::../api/protos/vkDestroyQueryPool.txt[]
* pname:device is the logical device that destroys the query pool.
* pname:queryPool is the query pool to destroy.
* pname:pAllocator controls host memory allocation as described in the
<<memory-allocation, Memory Allocation>> chapter.
.Valid Usage
****
* [[VUID-vkDestroyQueryPool-queryPool-00793]]
All submitted commands that refer to pname:queryPool must: have
completed execution
* [[VUID-vkDestroyQueryPool-queryPool-00794]]
If sname:VkAllocationCallbacks were provided when pname:queryPool was
created, a compatible set of callbacks must: be provided here
* [[VUID-vkDestroyQueryPool-queryPool-00795]]
If no sname:VkAllocationCallbacks were provided when pname:queryPool was
created, pname:pAllocator must: be `NULL`
****
include::../validity/protos/vkDestroyQueryPool.txt[]
--
[open,refpage='VkQueryType',desc='Specify the type of queries managed by a query pool',type='enums']
--
Possible values of slink:VkQueryPoolCreateInfo::pname:queryType, specifying
the type of queries managed by the pool, are:
include::../api/enums/VkQueryType.txt[]
* ename:VK_QUERY_TYPE_OCCLUSION specifies an <<queries-occlusion,
occlusion query>>.
* ename:VK_QUERY_TYPE_PIPELINE_STATISTICS specifies a <<queries-pipestats,
pipeline statistics query>>.
* ename:VK_QUERY_TYPE_TIMESTAMP specifies a <<queries-timestamps,
timestamp query>>.
--
[[queries-operation]]
== Query Operation
The operation of queries is controlled by the commands
flink:vkCmdBeginQuery, flink:vkCmdEndQuery, flink:vkCmdResetQueryPool,
flink:vkCmdCopyQueryPoolResults, and flink:vkCmdWriteTimestamp.
In order for a sname:VkCommandBuffer to record query management commands,
the queue family for which its sname:VkCommandPool was created must: support
the appropriate type of operations (graphics, compute) suitable for the
query type of a given query pool.
Each query in a query pool has a status that is either _unavailable_ or
_available_, and also has state to store the numerical results of a query
operation of the type requested when the query pool was created.
Resetting a query via flink:vkCmdResetQueryPool sets the status to
unavailable and makes the numerical results undefined:.
Performing a query operation with flink:vkCmdBeginQuery and
flink:vkCmdEndQuery changes the status to available when the query
<<queries-operation-finished,finishes>>, and updates the numerical results.
Both the availability status and numerical results are retrieved by calling
either flink:vkGetQueryPoolResults or flink:vkCmdCopyQueryPoolResults.
[[queries-order]]
Query commands, for the same query and submitted to the same queue, execute
in their entirety in <<synchronization-submission-order, submission order>>,
relative to each other.
In effect there is an implicit execution dependency from each such query
command to all query command previously submitted to the same queue.
There is one significant exception to this; if the pname:flags parameter of
flink:vkCmdCopyQueryPoolResults does not include
ename:VK_QUERY_RESULT_WAIT_BIT, execution of flink:vkCmdCopyQueryPoolResults
may: happen-before the results of flink:vkCmdEndQuery are available.
After query pool creation, each query is in an undefined: state and must: be
reset prior to use.
Queries must: also be reset between uses.
Using a query that has not been reset will result in undefined: behavior.
ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
If a logical device includes multiple physical devices, then each command
that writes a query must: execute on a single physical device, and any call
to flink:vkCmdBeginQuery must: execute the corresponding flink:vkCmdEndQuery
command on the same physical device.
endif::VK_VERSION_1_1,VK_KHR_device_group[]
[open,refpage='vkCmdResetQueryPool',desc='Reset queries in a query pool',type='protos']
--
To reset a range of queries in a query pool, call:
include::../api/protos/vkCmdResetQueryPool.txt[]
* pname:commandBuffer is the command buffer into which this command will
be recorded.
* pname:queryPool is the handle of the query pool managing the queries
being reset.
* pname:firstQuery is the initial query index to reset.
* pname:queryCount is the number of queries to reset.
When executed on a queue, this command sets the status of query indices
[eq]#[pname:firstQuery, pname:firstQuery {plus} pname:queryCount - 1]# to
unavailable.
.Valid Usage
****
* [[VUID-vkCmdResetQueryPool-firstQuery-00796]]
pname:firstQuery must: be less than the number of queries in
pname:queryPool
* [[VUID-vkCmdResetQueryPool-firstQuery-00797]]
The sum of pname:firstQuery and pname:queryCount must: be less than or
equal to the number of queries in pname:queryPool
****
include::../validity/protos/vkCmdResetQueryPool.txt[]
--
Once queries are reset and ready for use, query commands can: be issued to a
command buffer.
Occlusion queries and pipeline statistics queries count events - drawn
samples and pipeline stage invocations, respectively - resulting from
commands that are recorded between a flink:vkCmdBeginQuery command and a
flink:vkCmdEndQuery command within a specified command buffer, effectively
scoping a set of drawing and/or compute commands.
Timestamp queries write timestamps to a query pool.
A query must: begin and end in the same command buffer, although if it is a
primary command buffer, and the
<<features-features-inheritedQueries,inherited queries>> feature is enabled,
it can: execute secondary command buffers during the query operation.
For a secondary command buffer to be executed while a query is active, it
must: set the pname:occlusionQueryEnable, pname:queryFlags, and/or
pname:pipelineStatistics members of slink:VkCommandBufferInheritanceInfo to
conservative values, as described in the <<commandbuffers-recording, Command
Buffer Recording>> section.
A query must: either begin and end inside the same subpass of a render pass
instance, or must: both begin and end outside of a render pass instance
(i.e. contain entire render pass instances).
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
If queries are used while executing a render pass instance that has
multiview enabled, the query uses [eq]#N# consecutive query indices in the
query pool (starting at pname:query) where [eq]#N# is the number of bits set
in the view mask in the subpass the query is used in.
How the numerical results of the query are distributed among the queries is
implementation-dependent.
For example, some implementations may: write each view's results to a
distinct query, while other implementations may: write the total result to
the first query and write zero to the other queries.
However, the sum of the results in all the queries must: accurately reflect
the total result of the query summed over all views.
Applications can: sum the results from all the queries to compute the total
result.
Queries used with multiview rendering must: not span subpasses, i.e. they
must: begin and end in the same subpass.
endif::VK_VERSION_1_1,VK_KHR_multiview[]
[open,refpage='vkCmdBeginQuery',desc='Begin a query',type='protos']
--
To begin a query, call:
include::../api/protos/vkCmdBeginQuery.txt[]
* pname:commandBuffer is the command buffer into which this command will
be recorded.
* pname:queryPool is the query pool that will manage the results of the
query.
* pname:query is the query index within the query pool that will contain
the results.
* pname:flags is a bitmask of elink:VkQueryControlFlagBits specifying
constraints on the types of queries that can: be performed.
If the pname:queryType of the pool is ename:VK_QUERY_TYPE_OCCLUSION and
pname:flags contains ename:VK_QUERY_CONTROL_PRECISE_BIT, an implementation
must: return a result that matches the actual number of samples passed.
This is described in more detail in <<queries-occlusion,Occlusion Queries>>.
[[queries-operation-active]]
After beginning a query, that query is considered _active_ within the
command buffer it was called in until that same query is ended.
Queries active in a primary command buffer when secondary command buffers
are executed are considered active for those secondary command buffers.
.Valid Usage
****
* [[VUID-vkCmdBeginQuery-queryPool-01922]]
pname:queryPool must: have been created with a pname:queryType that
differs from that of any queries that are
<<queries-operation-active,active>> within pname:commandBuffer
* [[VUID-vkCmdBeginQuery-None-00807]]
All queries used by the command must: be unavailable
* [[VUID-vkCmdBeginQuery-queryType-00800]]
If the <<features-features-occlusionQueryPrecise,precise occlusion
queries>> feature is not enabled, or the pname:queryType used to create
pname:queryPool was not ename:VK_QUERY_TYPE_OCCLUSION, pname:flags must:
not contain ename:VK_QUERY_CONTROL_PRECISE_BIT
* [[VUID-vkCmdBeginQuery-query-00802]]
pname:query must: be less than the number of queries in pname:queryPool
* [[VUID-vkCmdBeginQuery-queryType-00803]]
If the pname:queryType used to create pname:queryPool was
ename:VK_QUERY_TYPE_OCCLUSION, the sname:VkCommandPool that
pname:commandBuffer was allocated from must: support graphics operations
* [[VUID-vkCmdBeginQuery-queryType-00804]]
If the pname:queryType used to create pname:queryPool was
ename:VK_QUERY_TYPE_PIPELINE_STATISTICS and any of the
pname:pipelineStatistics indicate graphics operations, the
sname:VkCommandPool that pname:commandBuffer was allocated from must:
support graphics operations
* [[VUID-vkCmdBeginQuery-queryType-00805]]
If the pname:queryType used to create pname:queryPool was
ename:VK_QUERY_TYPE_PIPELINE_STATISTICS and any of the
pname:pipelineStatistics indicate compute operations, the
sname:VkCommandPool that pname:commandBuffer was allocated from must:
support compute operations
ifdef::VK_VERSION_1_1[]
* [[VUID-vkCmdBeginQuery-commandBuffer-01885]]
pname:commandBuffer must: not be a protected command buffer
endif::VK_VERSION_1_1[]
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
* [[VUID-vkCmdBeginQuery-query-00808]]
If fname:vkCmdBeginQuery is called within a render pass instance, the
sum of pname:query and the number of bits set in the current subpass's
view mask must: be less than or equal to the number of queries in
pname:queryPool
endif::VK_VERSION_1_1,VK_KHR_multiview[]
****
include::../validity/protos/vkCmdBeginQuery.txt[]
--
[open,refpage='VkQueryControlFlagBits',desc='Bitmask specifying constraints on a query',type='enums']
--
Bits which can: be set in flink:vkCmdBeginQuery::pname:flags, specifying
constraints on the types of queries that can: be performed, are:
include::../api/enums/VkQueryControlFlagBits.txt[]
* ename:VK_QUERY_CONTROL_PRECISE_BIT specifies the precision of
<<queries-occlusion, occlusion queries>>.
--
[open,refpage='VkQueryControlFlags',desc='Bitmask of VkQueryControlFlagBits',type='enums']
--
include::../api/flags/VkQueryControlFlags.txt[]
sname:VkQueryControlFlags is a bitmask type for setting a mask of zero or
more slink:VkQueryControlFlagBits.
--
[open,refpage='vkCmdEndQuery',desc='Ends a query',type='protos']
--
To end a query after the set of desired draw or dispatch commands is
executed, call:
include::../api/protos/vkCmdEndQuery.txt[]
* pname:commandBuffer is the command buffer into which this command will
be recorded.
* pname:queryPool is the query pool that is managing the results of the
query.
* pname:query is the query index within the query pool where the result is
stored.
[[queries-operation-finished]]
As queries operate asynchronously, ending a query does not immediately set
the query's status to available.
A query is considered _finished_ when the final results of the query are
ready to be retrieved by flink:vkGetQueryPoolResults and
flink:vkCmdCopyQueryPoolResults, and this is when the query's status is set
to available.
Once a query is ended the query must: finish in finite time, unless the
state of the query is changed using other commands, e.g. by issuing a reset
of the query.
.Valid Usage
****
* [[VUID-vkCmdEndQuery-None-01923]]
All queries used by the command must: be
<<queries-operation-active,active>>
* [[VUID-vkCmdEndQuery-query-00810]]
pname:query must: be less than the number of queries in pname:queryPool
ifdef::VK_VERSION_1_1[]
* [[VUID-vkCmdEndQuery-commandBuffer-01886]]
pname:commandBuffer must: not be a protected command buffer
endif::VK_VERSION_1_1[]
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
* [[VUID-vkCmdEndQuery-query-00812]]
If fname:vkCmdEndQuery is called within a render pass instance, the sum
of pname:query and the number of bits set in the current subpass's view
mask must: be less than or equal to the number of queries in
pname:queryPool
endif::VK_VERSION_1_1,VK_KHR_multiview[]
****
include::../validity/protos/vkCmdEndQuery.txt[]
--
[[queries-operation-memorylayout]]
An application can: retrieve results either by requesting they be written
into application-provided memory, or by requesting they be copied into a
sname:VkBuffer.
In either case, the layout in memory is defined as follows:
* The first query's result is written starting at the first byte requested
by the command, and each subsequent query's result begins pname:stride
bytes later.
* Each query's result is a tightly packed array of unsigned integers,
either 32- or 64-bits as requested by the command, storing the numerical
results and, if requested, the availability status.
* If ename:VK_QUERY_RESULT_WITH_AVAILABILITY_BIT is used, the final
element of each query's result is an integer indicating whether the
query's result is available, with any non-zero value indicating that it
is available.
* Occlusion queries write one integer value - the number of samples
passed.
Pipeline statistics queries write one integer value for each bit that is
enabled in the pname:pipelineStatistics when the pool is created, and
the statistics values are written in bit order starting from the least
significant bit.
Timestamps write one integer value.
* If more than one query is retrieved and pname:stride is not at least as
large as the size of the array of integers corresponding to a single
query, the values written to memory are undefined:.
[open,refpage='vkGetQueryPoolResults',desc='Copy results of queries in a query pool to a host memory region',type='protos']
--
To retrieve status and results for a set of queries, call:
include::../api/protos/vkGetQueryPoolResults.txt[]
* pname:device is the logical device that owns the query pool.
* pname:queryPool is the query pool managing the queries containing the
desired results.
* pname:firstQuery is the initial query index.
* pname:queryCount is the number of queries.
pname:firstQuery and pname:queryCount together define a range of
queries.
For pipeline statistics queries, each query index in the pool contains
one integer value for each bit that is enabled in
slink:VkQueryPoolCreateInfo::pname:pipelineStatistics when the pool is
created.
* pname:dataSize is the size in bytes of the buffer pointed to by
pname:pData.
* pname:pData is a pointer to a user-allocated buffer where the results
will be written
* pname:stride is the stride in bytes between results for individual
queries within pname:pData.
* pname:flags is a bitmask of elink:VkQueryResultFlagBits specifying how
and when results are returned.
If no bits are set in pname:flags, and all requested queries are in the
available state, results are written as an array of 32-bit unsigned integer
values.
The behavior when not all queries are available, is described
<<queries-wait-bit-not-set, below>>.
If ename:VK_QUERY_RESULT_64_BIT is not set and the result overflows a 32-bit
value, the value may: either wrap or saturate.
Similarly, if ename:VK_QUERY_RESULT_64_BIT is set and the result overflows a
64-bit value, the value may: either wrap or saturate.
If ename:VK_QUERY_RESULT_WAIT_BIT is set, Vulkan will wait for each query to
be in the available state before retrieving the numerical results for that
query.
In this case, fname:vkGetQueryPoolResults is guaranteed to succeed and
return ename:VK_SUCCESS if the queries become available in a finite time
(i.e. if they have been issued and not reset).
If queries will never finish (e.g. due to being reset but not issued), then
fname:vkGetQueryPoolResults may: not return in finite time.
[[queries-wait-bit-not-set]]
If ename:VK_QUERY_RESULT_WAIT_BIT and ename:VK_QUERY_RESULT_PARTIAL_BIT are
both not set then no result values are written to pname:pData for queries
that are in the unavailable state at the time of the call, and
fname:vkGetQueryPoolResults returns ename:VK_NOT_READY.
However, availability state is still written to pname:pData for those
queries if ename:VK_QUERY_RESULT_WITH_AVAILABILITY_BIT is set.
[NOTE]
.Note
====
Applications must: take care to ensure that use of the
ename:VK_QUERY_RESULT_WAIT_BIT bit has the desired effect.
For example, if a query has been used previously and a command buffer
records the commands fname:vkCmdResetQueryPool, fname:vkCmdBeginQuery, and
fname:vkCmdEndQuery for that query, then the query will remain in the
available state until the fname:vkCmdResetQueryPool command executes on a
queue.
Applications can: use fences or events to ensure that a query has already
been reset before checking for its results or availability status.
Otherwise, a stale value could be returned from a previous use of the query.
The above also applies when ename:VK_QUERY_RESULT_WAIT_BIT is used in
combination with ename:VK_QUERY_RESULT_WITH_AVAILABILITY_BIT.
In this case, the returned availability status may: reflect the result of a
previous use of the query unless the fname:vkCmdResetQueryPool command has
been executed since the last use of the query.
====
[NOTE]
.Note
====
Applications can: double-buffer query pool usage, with a pool per frame, and
reset queries at the end of the frame in which they are read.
====
If ename:VK_QUERY_RESULT_PARTIAL_BIT is set, ename:VK_QUERY_RESULT_WAIT_BIT
is not set, and the query's status is unavailable, an intermediate result
value between zero and the final result value is written to pname:pData for
that query.
ename:VK_QUERY_RESULT_PARTIAL_BIT must: not be used if the pool's
pname:queryType is ename:VK_QUERY_TYPE_TIMESTAMP.
If ename:VK_QUERY_RESULT_WITH_AVAILABILITY_BIT is set, the final integer
value written for each query is non-zero if the query's status was available
or zero if the status was unavailable.
When ename:VK_QUERY_RESULT_WITH_AVAILABILITY_BIT is used, implementations
must: guarantee that if they return a non-zero availability value then the
numerical results must: be valid, assuming the results are not reset by a
subsequent command.
[NOTE]
.Note
====
Satisfying this guarantee may: require careful ordering by the application,
e.g. to read the availability status before reading the results.
====
.Valid Usage
****
* [[VUID-vkGetQueryPoolResults-firstQuery-00813]]
pname:firstQuery must: be less than the number of queries in
pname:queryPool
* [[VUID-vkGetQueryPoolResults-flags-00814]]
If ename:VK_QUERY_RESULT_64_BIT is not set in pname:flags then
pname:pData and pname:stride must: be multiples of `4`
* [[VUID-vkGetQueryPoolResults-flags-00815]]
If ename:VK_QUERY_RESULT_64_BIT is set in pname:flags then pname:pData
and pname:stride must: be multiples of `8`
* [[VUID-vkGetQueryPoolResults-firstQuery-00816]]
The sum of pname:firstQuery and pname:queryCount must: be less than or
equal to the number of queries in pname:queryPool
* [[VUID-vkGetQueryPoolResults-dataSize-00817]]
pname:dataSize must: be large enough to contain the result of each
query, as described <<queries-operation-memorylayout,here>>
* [[VUID-vkGetQueryPoolResults-queryType-00818]]
If the pname:queryType used to create pname:queryPool was
ename:VK_QUERY_TYPE_TIMESTAMP, pname:flags must: not contain
ename:VK_QUERY_RESULT_PARTIAL_BIT
****
include::../validity/protos/vkGetQueryPoolResults.txt[]
--
[open,refpage='VkQueryResultFlagBits',desc='Bitmask specifying how and when query results are returned',type='enums']
--
Bits which can: be set in flink:vkGetQueryPoolResults::pname:flags and
flink:vkCmdCopyQueryPoolResults::pname:flags, specifying how and when
results are returned, are:
include::../api/enums/VkQueryResultFlagBits.txt[]
* ename:VK_QUERY_RESULT_64_BIT specifies the results will be written as an
array of 64-bit unsigned integer values.
If this bit is not set, the results will be written as an array of
32-bit unsigned integer values.
* ename:VK_QUERY_RESULT_WAIT_BIT specifies that Vulkan will wait for each
query's status to become available before retrieving its results.
* ename:VK_QUERY_RESULT_WITH_AVAILABILITY_BIT specifies that the
availability status accompanies the results.
* ename:VK_QUERY_RESULT_PARTIAL_BIT specifies that returning partial
results is acceptable.
--
[open,refpage='VkQueryResultFlags',desc='Bitmask of VkQueryResultFlagBits',type='enums']
--
include::../api/flags/VkQueryResultFlags.txt[]
sname:VkQueryResultFlags is a bitmask type for setting a mask of zero or
more slink:VkQueryResultFlagBits.
--
[open,refpage='vkCmdCopyQueryPoolResults',desc='Copy the results of queries in a query pool to a buffer object',type='protos']
--
To copy query statuses and numerical results directly to buffer memory,
call:
include::../api/protos/vkCmdCopyQueryPoolResults.txt[]
* pname:commandBuffer is the command buffer into which this command will
be recorded.
* pname:queryPool is the query pool managing the queries containing the
desired results.
* pname:firstQuery is the initial query index.
* pname:queryCount is the number of queries.
pname:firstQuery and pname:queryCount together define a range of
queries.
* pname:dstBuffer is a slink:VkBuffer object that will receive the results
of the copy command.
* pname:dstOffset is an offset into pname:dstBuffer.
* pname:stride is the stride in bytes between results for individual
queries within pname:dstBuffer.
The required size of the backing memory for pname:dstBuffer is
determined as described above for flink:vkGetQueryPoolResults.
* pname:flags is a bitmask of elink:VkQueryResultFlagBits specifying how
and when results are returned.
fname:vkCmdCopyQueryPoolResults is guaranteed to see the effect of previous
uses of fname:vkCmdResetQueryPool in the same queue, without any additional
synchronization.
Thus, the results will always reflect the most recent use of the query.
pname:flags has the same possible values described above for the pname:flags
parameter of flink:vkGetQueryPoolResults, but the different style of
execution causes some subtle behavioral differences.
Because fname:vkCmdCopyQueryPoolResults executes in order with respect to
other query commands, there is less ambiguity about which use of a query is
being requested.
If no bits are set in pname:flags, results for all requested queries in the
available state are written as 32-bit unsigned integer values, and nothing
is written for queries in the unavailable state.
If ename:VK_QUERY_RESULT_64_BIT is set, the results are written as an array
of 64-bit unsigned integer values as described for
flink:vkGetQueryPoolResults.
If ename:VK_QUERY_RESULT_WAIT_BIT is set, the implementation will wait for
each query's status to be in the available state before retrieving the
numerical results for that query.
This is guaranteed to reflect the most recent use of the query on the same
queue, assuming that the query is not being simultaneously used by other
queues.
If the query does not become available in a finite amount of time (e.g. due
to not issuing a query since the last reset), a ename:VK_ERROR_DEVICE_LOST
error may: occur.
Similarly, if ename:VK_QUERY_RESULT_WITH_AVAILABILITY_BIT is set and
ename:VK_QUERY_RESULT_WAIT_BIT is not set, the availability is guaranteed to
reflect the most recent use of the query on the same queue, assuming that
the query is not being simultaneously used by other queues.
As with fname:vkGetQueryPoolResults, implementations must: guarantee that if
they return a non-zero availability value, then the numerical results are
valid.
If ename:VK_QUERY_RESULT_PARTIAL_BIT is set, ename:VK_QUERY_RESULT_WAIT_BIT
is not set, and the query's status is unavailable, an intermediate result
value between zero and the final result value is written for that query.
ename:VK_QUERY_RESULT_PARTIAL_BIT must: not be used if the pool's
pname:queryType is ename:VK_QUERY_TYPE_TIMESTAMP.
fname:vkCmdCopyQueryPoolResults is considered to be a transfer operation,
and its writes to buffer memory must: be synchronized using
ename:VK_PIPELINE_STAGE_TRANSFER_BIT and ename:VK_ACCESS_TRANSFER_WRITE_BIT
before using the results.
.Valid Usage
****
* [[VUID-vkCmdCopyQueryPoolResults-dstOffset-00819]]
pname:dstOffset must: be less than the size of pname:dstBuffer
* [[VUID-vkCmdCopyQueryPoolResults-firstQuery-00820]]
pname:firstQuery must: be less than the number of queries in
pname:queryPool
* [[VUID-vkCmdCopyQueryPoolResults-firstQuery-00821]]
The sum of pname:firstQuery and pname:queryCount must: be less than or
equal to the number of queries in pname:queryPool
* [[VUID-vkCmdCopyQueryPoolResults-flags-00822]]
If ename:VK_QUERY_RESULT_64_BIT is not set in pname:flags then
pname:dstOffset and pname:stride must: be multiples of `4`
* [[VUID-vkCmdCopyQueryPoolResults-flags-00823]]
If ename:VK_QUERY_RESULT_64_BIT is set in pname:flags then
pname:dstOffset and pname:stride must: be multiples of `8`
* [[VUID-vkCmdCopyQueryPoolResults-dstBuffer-00824]]
pname:dstBuffer must: have enough storage, from pname:dstOffset, to
contain the result of each query, as described
<<queries-operation-memorylayout,here>>
* [[VUID-vkCmdCopyQueryPoolResults-dstBuffer-00825]]
pname:dstBuffer must: have been created with
ename:VK_BUFFER_USAGE_TRANSFER_DST_BIT usage flag
* [[VUID-vkCmdCopyQueryPoolResults-dstBuffer-00826]]
If pname:dstBuffer is non-sparse then it must: be bound completely and
contiguously to a single sname:VkDeviceMemory object
* [[VUID-vkCmdCopyQueryPoolResults-queryType-00827]]
If the pname:queryType used to create pname:queryPool was
ename:VK_QUERY_TYPE_TIMESTAMP, pname:flags must: not contain
ename:VK_QUERY_RESULT_PARTIAL_BIT
****
include::../validity/protos/vkCmdCopyQueryPoolResults.txt[]
--
[[queries-operation-undefined]]
Rendering operations such as clears, MSAA resolves, attachment load/store
operations, and blits may: count towards the results of queries.
This behavior is implementation-dependent and may: vary depending on the
path used within an implementation.
For example, some implementations have several types of clears, some of
which may: include vertices and some not.
[[queries-occlusion]]
== Occlusion Queries
Occlusion queries track the number of samples that pass the per-fragment
tests for a set of drawing commands.
As such, occlusion queries are only available on queue families supporting
graphics operations.
The application can: then use these results to inform future rendering
decisions.
An occlusion query is begun and ended by calling fname:vkCmdBeginQuery and
fname:vkCmdEndQuery, respectively.
When an occlusion query begins, the count of passing samples always starts
at zero.
For each drawing command, the count is incremented as described in
<<fragops-samplecount,Sample Counting>>.
If pname:flags does not contain ename:VK_QUERY_CONTROL_PRECISE_BIT an
implementation may: generate any non-zero result value for the query if the
count of passing samples is non-zero.
[NOTE]
.Note
====
Not setting ename:VK_QUERY_CONTROL_PRECISE_BIT mode may: be more efficient
on some implementations, and should: be used where it is sufficient to know
a boolean result on whether any samples passed the per-fragment tests.
In this case, some implementations may: only return zero or one, indifferent
to the actual number of samples passing the per-fragment tests.
====
When an occlusion query finishes, the result for that query is marked as
available.
The application can: then either copy the result to a buffer (via
fname:vkCmdCopyQueryPoolResults) or request it be put into host memory (via
fname:vkGetQueryPoolResults).
[NOTE]
.Note
====
If occluding geometry is not drawn first, samples can: pass the depth test,
but still not be visible in a final image.
====
[[queries-pipestats]]
== Pipeline Statistics Queries
Pipeline statistics queries allow the application to sample a specified set
of sname:VkPipeline counters.
These counters are accumulated by Vulkan for a set of either draw or
dispatch commands while a pipeline statistics query is active.
As such, pipeline statistics queries are available on queue families
supporting either graphics or compute operations.
Further, the availability of pipeline statistics queries is indicated by the
pname:pipelineStatisticsQuery member of the sname:VkPhysicalDeviceFeatures
object (see fname:vkGetPhysicalDeviceFeatures and fname:vkCreateDevice for
detecting and requesting this query type on a sname:VkDevice).
A pipeline statistics query is begun and ended by calling
fname:vkCmdBeginQuery and fname:vkCmdEndQuery, respectively.
When a pipeline statistics query begins, all statistics counters are set to
zero.
While the query is active, the pipeline type determines which set of
statistics are available, but these must: be configured on the query pool
when it is created.
If a statistic counter is issued on a command buffer that does not support
the corresponding operation, the value of that counter is undefined: after
the query has finished.
At least one statistic counter relevant to the operations supported on the
recording command buffer must: be enabled.
[open,refpage='VkQueryPipelineStatisticFlagBits',desc='Bitmask specifying queried pipeline statistics',type='enums']
--
Bits which can: be set to individually enable pipeline statistics counters
for query pools with slink:VkQueryPoolCreateInfo::pname:pipelineStatistics,
and for secondary command buffers with
slink:VkCommandBufferInheritanceInfo::pname:pipelineStatistics, are:
include::../api/enums/VkQueryPipelineStatisticFlagBits.txt[]
* ename:VK_QUERY_PIPELINE_STATISTIC_INPUT_ASSEMBLY_VERTICES_BIT specifies
that queries managed by the pool will count the number of vertices
processed by the <<drawing,input assembly>> stage.
Vertices corresponding to incomplete primitives may: contribute to the
count.
* ename:VK_QUERY_PIPELINE_STATISTIC_INPUT_ASSEMBLY_PRIMITIVES_BIT
specifies that queries managed by the pool will count the number of
primitives processed by the <<drawing,input assembly>> stage.
If primitive restart is enabled, restarting the primitive topology has
no effect on the count.
Incomplete primitives may: be counted.
* ename:VK_QUERY_PIPELINE_STATISTIC_VERTEX_SHADER_INVOCATIONS_BIT
specifies that queries managed by the pool will count the number of
vertex shader invocations.
This counter's value is incremented each time a vertex shader is
<<shaders-vertex-execution,invoked>>.
* ename:VK_QUERY_PIPELINE_STATISTIC_GEOMETRY_SHADER_INVOCATIONS_BIT
specifies that queries managed by the pool will count the number of
geometry shader invocations.
This counter's value is incremented each time a geometry shader is
<<shaders-geometry-execution,invoked>>.
In the case of <<geometry-invocations,instanced geometry shaders>>, the
geometry shader invocations count is incremented for each separate
instanced invocation.
* ename:VK_QUERY_PIPELINE_STATISTIC_GEOMETRY_SHADER_PRIMITIVES_BIT
specifies that queries managed by the pool will count the number of
primitives generated by geometry shader invocations.
The counter's value is incremented each time the geometry shader emits a
primitive.
Restarting primitive topology using the SPIR-V instructions
code:OpEndPrimitive or code:OpEndStreamPrimitive has no effect on the
geometry shader output primitives count.
* ename:VK_QUERY_PIPELINE_STATISTIC_CLIPPING_INVOCATIONS_BIT specifies
that queries managed by the pool will count the number of primitives
processed by the <<vertexpostproc-clipping,Primitive Clipping>> stage of
the pipeline.
The counter's value is incremented each time a primitive reaches the
primitive clipping stage.
* ename:VK_QUERY_PIPELINE_STATISTIC_CLIPPING_PRIMITIVES_BIT specifies that
queries managed by the pool will count the number of primitives output
by the <<vertexpostproc-clipping,Primitive Clipping>> stage of the
pipeline.
The counter's value is incremented each time a primitive passes the
primitive clipping stage.
The actual number of primitives output by the primitive clipping stage
for a particular input primitive is implementation-dependent but must:
satisfy the following conditions:
** If at least one vertex of the input primitive lies inside the clipping
volume, the counter is incremented by one or more.
** Otherwise, the counter is incremented by zero or more.
* ename:VK_QUERY_PIPELINE_STATISTIC_FRAGMENT_SHADER_INVOCATIONS_BIT
specifies that queries managed by the pool will count the number of
fragment shader invocations.
The counter's value is incremented each time the fragment shader is
<<shaders-fragment-execution,invoked>>.
* ename:VK_QUERY_PIPELINE_STATISTIC_TESSELLATION_CONTROL_SHADER_PATCHES_BIT
specifies that queries managed by the pool will count the number of
patches processed by the tessellation control shader.
The counter's value is incremented once for each patch for which a
tessellation control shader is
<<shaders-tessellation-control-execution,invoked>>.
* ename:VK_QUERY_PIPELINE_STATISTIC_TESSELLATION_EVALUATION_SHADER_INVOCATIONS_BIT
specifies that queries managed by the pool will count the number of
invocations of the tessellation evaluation shader.
The counter's value is incremented each time the tessellation evaluation
shader is <<shaders-tessellation-evaluation-execution,invoked>>.
* ename:VK_QUERY_PIPELINE_STATISTIC_COMPUTE_SHADER_INVOCATIONS_BIT
specifies that queries managed by the pool will count the number of
compute shader invocations.
The counter's value is incremented every time the compute shader is
invoked.
Implementations may: skip the execution of certain compute shader
invocations or execute additional compute shader invocations for
implementation-dependent reasons as long as the results of rendering
otherwise remain unchanged.
These values are intended to measure relative statistics on one
implementation.
Various device architectures will count these values differently.
Any or all counters may: be affected by the issues described in
<<queries-operation-undefined,Query Operation>>.
[NOTE]
.Note
====
For example, tile-based rendering devices may: need to replay the scene
multiple times, affecting some of the counts.
====
If a pipeline has pname:rasterizerDiscardEnable enabled, implementations
may: discard primitives after the final vertex processing stage.
As a result, if pname:rasterizerDiscardEnable is enabled, the clipping input
and output primitives counters may: not be incremented.
When a pipeline statistics query finishes, the result for that query is
marked as available.
The application can: copy the result to a buffer (via
fname:vkCmdCopyQueryPoolResults), or request it be put into host memory (via
fname:vkGetQueryPoolResults).
--
[open,refpage='VkQueryPipelineStatisticFlags',desc='Bitmask of VkQueryPipelineStatisticFlagBits',type='enums']
--
include::../api/flags/VkQueryPipelineStatisticFlags.txt[]
sname:VkQueryPipelineStatisticFlags is a bitmask type for setting a mask of
zero or more slink:VkQueryPipelineStatisticFlagBits.
--
[[queries-timestamps]]
== Timestamp Queries
_Timestamps_ provide applications with a mechanism for timing the execution
of commands.
A timestamp is an integer value generated by the sname:VkPhysicalDevice.
Unlike other queries, timestamps do not operate over a range, and so do not
use flink:vkCmdBeginQuery or flink:vkCmdEndQuery.
The mechanism is built around a set of commands that allow the application
to tell the sname:VkPhysicalDevice to write timestamp values to a
<<queries-pools,query pool>> and then either read timestamp values on the
host (using flink:vkGetQueryPoolResults) or copy timestamp values to a
sname:VkBuffer (using flink:vkCmdCopyQueryPoolResults).
The application can: then compute differences between timestamps to
determine execution time.
The number of valid bits in a timestamp value is determined by the
sname:VkQueueFamilyProperties::pname:timestampValidBits property of the
queue on which the timestamp is written.
Timestamps are supported on any queue which reports a non-zero value for
pname:timestampValidBits via flink:vkGetPhysicalDeviceQueueFamilyProperties.
If the <<features-limits-timestampComputeAndGraphics,
pname:timestampComputeAndGraphics>> limit is ename:VK_TRUE, timestamps are
supported by every queue family that supports either graphics or compute
operations (see slink:VkQueueFamilyProperties).
The number of nanoseconds it takes for a timestamp value to be incremented
by 1 can: be obtained from
sname:VkPhysicalDeviceLimits::pname:timestampPeriod after a call to
fname:vkGetPhysicalDeviceProperties.
[open,refpage='vkCmdWriteTimestamp',desc='Write a device timestamp into a query object',type='protos']
--
To request a timestamp, call:
include::../api/protos/vkCmdWriteTimestamp.txt[]
* pname:commandBuffer is the command buffer into which the command will be
recorded.
* pname:pipelineStage is one of the elink:VkPipelineStageFlagBits,
specifying a stage of the pipeline.
* pname:queryPool is the query pool that will manage the timestamp.
* pname:query is the query within the query pool that will contain the
timestamp.
fname:vkCmdWriteTimestamp latches the value of the timer when all previous
commands have completed executing as far as the specified pipeline stage,
and writes the timestamp value to memory.
When the timestamp value is written, the availability status of the query is
set to available.
[NOTE]
.Note
====
If an implementation is unable to detect completion and latch the timer at
any specific stage of the pipeline, it may: instead do so at any logically
later stage.
====
flink:vkCmdCopyQueryPoolResults can: then be called to copy the timestamp
value from the query pool into buffer memory, with ordering and
synchronization behavior equivalent to how other queries operate.
Timestamp values can: also be retrieved from the query pool using
flink:vkGetQueryPoolResults.
As with other queries, the query must: be reset using
flink:vkCmdResetQueryPool before requesting the timestamp value be written
to it.
While fname:vkCmdWriteTimestamp can: be called inside or outside of a render
pass instance, flink:vkCmdCopyQueryPoolResults must: only be called outside
of a render pass instance.
Timestamps may: only be meaningfully compared if they are written by
commands submitted to the same queue.
[NOTE]
.Note
====
An example of such a comparison is determining the execution time of a
sequence of commands.
====
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
If fname:vkCmdWriteTimestamp is called while executing a render pass
instance that has multiview enabled, the timestamp uses [eq]#N# consecutive
query indices in the query pool (starting at pname:query) where [eq]#N# is
the number of bits set in the view mask of the subpass the command is
executed in.
The resulting query values are determined by an implementation-dependent
choice of one of the following behaviors:
* The first query is a timestamp value and (if more than one bit is set in
the view mask) zero is written to the remaining queries.
If two timestamps are written in the same subpass, the sum of the
execution time of all views between those commands is the difference
between the first query written by each command.
* All [eq]#N# queries are timestamp values.
If two timestamps are written in the same subpass, the sum of the
execution time of all views between those commands is the sum of the
difference between corresponding queries written by each command.
The difference between corresponding queries may: be the execution time
of a single view.
In either case, the application can: sum the differences between all [eq]#N#
queries to determine the total execution time.
endif::VK_VERSION_1_1,VK_KHR_multiview[]
.Valid Usage
****
* [[VUID-vkCmdWriteTimestamp-queryPool-01416]]
pname:queryPool must: have been created with a pname:queryType of
ename:VK_QUERY_TYPE_TIMESTAMP
* [[VUID-vkCmdWriteTimestamp-queryPool-00828]]
The query identified by pname:queryPool and pname:query must: be
_unavailable_
* [[VUID-vkCmdWriteTimestamp-timestampValidBits-00829]]
The command pool's queue family must: support a non-zero
pname:timestampValidBits
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
* [[VUID-vkCmdWriteTimestamp-None-00830]]
All queries used by the command must: be unavailable
* [[VUID-vkCmdWriteTimestamp-query-00831]]
If fname:vkCmdWriteTimestamp is called within a render pass instance,
the sum of pname:query and the number of bits set in the current
subpass's view mask must: be less than or equal to the number of queries
in pname:queryPool
endif::VK_VERSION_1_1,VK_KHR_multiview[]
****
include::../validity/protos/vkCmdWriteTimestamp.txt[]
--
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