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Vulkan-Docs/doc/specs/vulkan/chapters/queries.txt
Jon Leech 348990517c Change log for September 30, 2016 Vulkan 1.0.29 spec update: 
* Bump API patch number and header version number to 29 for this update.

Github Issues:

  * Remove redundant constraint on
    slink:VkCommandBufferInheritanceInfo::pname:queryFlags (public issue
    224).
  * Fix typo and remove link in Note in the
    <<extended-functionality-instance-extensions-and-devices, Instance
    Extensions and Device Extensions>> section (public issue 359).
  * Fix erroneous validation statement for the pname:layout member of
    slink:VkComputePipelineCreateInfo (public issue 362).

Internal Issues:

  * Restore long figure captions using asciidoc sidebar blocks, due to
    restrictions of asciidoc syntax (internal issue 101).
  * Replace most latexmath equations with comparable markup in straight
    asciidoc, which significantly improves time required to fully load and
    process the HTML forms of the Specification. There are known minor font
    and alignment inconsistencies with MathJax and PDF rendering of
    latexmath equations. Please do not file github issues about these. We
    are aware of the inconsistencies and will make refinements over time,
    while the performance improvements are compelling in at least some major
    browsers (internal issue 313).
  * Move handcoded validity statements from +vk.xml+ into the Specification
    body, easing work in the single-branch model. Specify the distinction
    between these explicit statements, and the implicit validity statements
    inferred from vk.xml. Validity statements now appear in two blocks for
    each command and structure - handcoded "Valid Usage" and the implicit
    "Valid Usage (Implicit)" (internal issue 392).
  * Add the +returnedonly="false"+ attribute to WSI output structures,
    removing incorrectly generated implicit validity statements for
    slink:VkDisplayPropertiesKHR, slink:VkDisplayPlanePropertiesKHR,
    slink:VkDisplayModePropertiesKHR, slink:VkDisplayPlaneCapabilitiesKHR,
    slink:VkSurfaceCapabilitiesKHR, and slink:VkSurfaceFormatKHR structures
    (internal issue 486).
  * Update slink:VkImageLayout to require the
    ename:VK_IMAGE_USAGE_SAMPLED_BIT be set for sampled depth/stencil images
    (internal issue 487).
  * Use an explicit format specifier string for the date command invocation
    in the +Makefile+ instead of the shorthand -R option, which doesn't work
    on BSD and MaxOS X date commands (internal issue 500).

Other Issues:

  * Use the terms ``allocation scope'' and ``extension scope'' instead of
    just ``scope'', and add them to the glossary.
2016-09-30 21:13:37 -07:00

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// Copyright (c) 2015-2016 The Khronos Group Inc.
// Copyright notice at https://www.khronos.org/registry/speccopyright.html
[[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
// refBegin VkQueryPool Opaque handle to a query pool object
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[]
// refEnd VkQueryPool
// refBegin vkCreateQueryPool Create a new query pool object
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 sname:VkQueryPool handle in which the
resulting query pool object is returned.
include::../validity/protos/vkCreateQueryPool.txt[]
// refBegin VkQueryPoolCreateInfo Structure specifying parameters of a newly created query pool
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 the type of queries managed by the pool, and must: be
one of the values
+
--
// refBegin VkQueryType Specify the type of queries managed by a query pool
include::../api/enums/VkQueryType.txt[]
--
* pname:queryCount is the number of queries managed by the pool.
* pname:pipelineStatistics is a bitmask indicating 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
****
* If the <<features-features-pipelineStatisticsQuery,pipeline statistics
queries>> feature is not enabled, pname:queryType must: not be
ename:VK_QUERY_TYPE_PIPELINE_STATISTICS
* 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[]
// refBegin vkDestroyQueryPool Destroy a query pool object
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
****
* All submitted commands that refer to pname:queryPool must: have
completed execution
* If sname:VkAllocationCallbacks were provided when pname:queryPool was
created, a compatible set of callbacks must: be provided here
* If no sname:VkAllocationCallbacks were provided when pname:queryPool was
created, pname:pAllocator must: be `NULL`
****
include::../validity/protos/vkDestroyQueryPool.txt[]
[[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.
All query commands execute in order and are guaranteed to see the effects of
each other's memory accesses, with one significant exception:
fname:vkCmdCopyQueryPoolResults may: execute before the results of
fname:vkCmdEndQuery are available.
However, if ename:VK_QUERY_RESULT_WAIT_BIT is used, then
fname:vkCmdCopyQueryPoolResults must: reflect the result of any previously
executed queries.
Other sequences of commands, such as fname:vkCmdResetQueryPool followed by
fname:vkCmdBeginQuery, must: make the effects of the first command visible
to the second command.
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.
// refBegin vkCmdResetQueryPool Reset queries in a query pool
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 + pname:queryCount - 1]# to
unavailable.
.Valid Usage
****
* pname:firstQuery must: be less than the number of queries in
pname:queryPool
* 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).
// refBegin vkCmdBeginQuery Begin a query
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 indicating constraints on the types of queries
that can: be performed.
Bits which can: be set include:
+
// refBegin VkQueryControlFlagBits Bitmask specifying constraints on a query
include::../api/enums/VkQueryControlFlagBits.txt[]
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
****
* The query identified by pname:queryPool and pname:query must: currently
not be <<queries-operation-active,active>>
* The query identified by pname:queryPool and pname:query must: be
unavailable
* 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
* pname:queryPool must: have been created with a pname:queryType that
differs from that of any other queries that have been made
<<queries-operation-active,active>>, and are currently still active
within pname:commandBuffer
* pname:query must: be less than the number of queries in pname:queryPool
* 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
* 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
* 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
****
include::../validity/protos/vkCmdBeginQuery.txt[]
// refBegin vkCmdEndQuery Ends a query
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
****
* The query identified by pname:queryPool and pname:query must: currently
be <<queries-operation-active,active>>
* pname:query must: be less than the number of queries in pname:queryPool
****
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.
// refBegin vkGetQueryPoolResults Copy results of queries in a query pool to a host memory region
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.
* 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.
Bits which can: be set include:
+
--
// refBegin VkQueryResultFlagBits Bitmask specifying how and when query results are returned
include::../api/enums/VkQueryResultFlagBits.txt[]
--
+
** ename:VK_QUERY_RESULT_64_BIT indicates 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 indicates that Vulkan will wait for each
query's status to become available before retrieving its results.
** ename:VK_QUERY_RESULT_WITH_AVAILABILITY_BIT indicates that the
availability status accompanies the results.
** ename:VK_QUERY_RESULT_PARTIAL_BIT indicates that returning partial
results is acceptable.
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
****
* pname:firstQuery must: be less than the number of queries in
pname:queryPool
* If ename:VK_QUERY_RESULT_64_BIT is not set in pname:flags then
pname:pData and pname:stride must: be multiples of `4`
* If ename:VK_QUERY_RESULT_64_BIT is set in pname:flags then pname:pData
and pname:stride must: be multiples of `8`
* The sum of pname:firstQuery and pname:queryCount must: be less than or
equal to the number of queries in pname:queryPool
* pname:dataSize must: be large enough to contain the result of each
query, as described <<queries-operation-memorylayout,here>>
* 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[]
// refBegin vkCmdCopyQueryPoolResults Copy the results of queries in a query pool to a buffer object
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 sname: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
****
* pname:dstOffset must: be less than the size of pname:dstBuffer
* pname:firstQuery must: be less than the number of queries in
pname:queryPool
* The sum of pname:firstQuery and pname:queryCount must: be less than or
equal to the number of queries in pname:queryPool
* If ename:VK_QUERY_RESULT_64_BIT is not set in pname:flags then
pname:dstOffset and pname:stride must: be multiples of `4`
* If ename:VK_QUERY_RESULT_64_BIT is set in pname:flags then
pname:dstOffset and pname:stride must: be multiples of `8`
* pname:dstBuffer must: have enough storage, from pname:dstOffset, to
contain the result of each query, as described
<<queries-operation-memorylayout,here>>
* pname:dstBuffer must: have been created with
ename:VK_BUFFER_USAGE_TRANSFER_DST_BIT usage flag
* 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, 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.
The pipeline statistic counters are individually enabled for query pools
with sname:VkQueryPoolCreateInfo::pname:pipelineStatistics, and for
secondary command buffers with
sname:VkCommandBufferInheritanceInfo::pname:pipelineStatistics.
// refBegin VkQueryPipelineStatisticFlagBits Bitmask specifying queried pipeline statistics
Bits which can: be set in pname:pipelineStatistics include:
include::../api/enums/VkQueryPipelineStatisticFlagBits.txt[]
These bits have the following meanings:
* If ename:VK_QUERY_PIPELINE_STATISTIC_INPUT_ASSEMBLY_VERTICES_BIT is set,
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.
* If ename:VK_QUERY_PIPELINE_STATISTIC_INPUT_ASSEMBLY_PRIMITIVES_BIT is
set, 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.
* If ename:VK_QUERY_PIPELINE_STATISTIC_VERTEX_SHADER_INVOCATIONS_BIT is
set, 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>>.
* If ename:VK_QUERY_PIPELINE_STATISTIC_GEOMETRY_SHADER_INVOCATIONS_BIT is
set, 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.
* If ename:VK_QUERY_PIPELINE_STATISTIC_GEOMETRY_SHADER_PRIMITIVES_BIT is
set, 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.
* If ename:VK_QUERY_PIPELINE_STATISTIC_CLIPPING_INVOCATIONS_BIT is set,
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.
* If ename:VK_QUERY_PIPELINE_STATISTIC_CLIPPING_PRIMITIVES_BIT is set,
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.
* If ename:VK_QUERY_PIPELINE_STATISTIC_FRAGMENT_SHADER_INVOCATIONS_BIT is
set, 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>>.
* If
ename:VK_QUERY_PIPELINE_STATISTIC_TESSELLATION_CONTROL_SHADER_PATCHES_BIT
is set, 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>>.
* If
ename:VK_QUERY_PIPELINE_STATISTIC_TESSELLATION_EVALUATION_SHADER_INVOCATIONS_BIT
is set, 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>>.
* If ename:VK_QUERY_PIPELINE_STATISTIC_COMPUTE_SHADER_INVOCATIONS_BIT is
set, 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).
// refEnd 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.
// refBegin vkCmdWriteTimestamp Write a device timestamp into a query object
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.
.Valid Usage
****
* The query identified by pname:queryPool and pname:query must: be
_unavailable_
* The command pool's queue family must: support a non-zero
pname:timestampValidBits
****
include::../validity/protos/vkCmdWriteTimestamp.txt[]
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