src/appendices/VK_KHR_performance_query.txt

// Copyright 2016-2021 The Khronos Group, Inc.
//
// SPDX-License-Identifier: CC-BY-4.0

include::{generated}/meta/{refprefix}VK_KHR_performance_query.txt[]

=== Other Extension Metadata

*Last Modified Date*::
    2019-10-08
*IP Status*::
    No known IP claims.
*Contributors*::
  - Jesse Barker, Unity Technologies
  - Kenneth Benzie, Codeplay
  - Jan-Harald Fredriksen, ARM
  - Jeff Leger, Qualcomm
  - Jesse Hall, Google
  - Tobias Hector, AMD
  - Neil Henning, Codeplay
  - Baldur Karlsson
  - Lionel Landwerlin, Intel
  - Peter Lohrmann, AMD
  - Alon Or-bach, Samsung
  - Daniel Rakos, AMD
  - Niklas Smedberg, Unity Technologies
  - Igor Ostrowski, Intel

=== Description

The `VK_KHR_performance_query` extension adds a mechanism to allow querying
of performance counters for use in applications and by profiling tools.

Each queue family may: expose counters that can: be enabled on a queue of
that family.
We extend elink:VkQueryType to add a new query type for performance queries,
and chain a structure on slink:VkQueryPoolCreateInfo to specify the
performance queries to enable.

include::{generated}/interfaces/VK_KHR_performance_query.txt[]

=== Issues

1) Should this extension include a mechanism to begin a query in command
buffer _A_ and end the query in command buffer _B_?

*RESOLVED* No - queries are tied to command buffer creation and thus have to
be encapsulated within a single command buffer.

2) Should this extension include a mechanism to begin and end queries
globally on the queue, not using the existing command buffer commands?

*RESOLVED* No - for the same reasoning as the resolution of 1).

3) Should this extension expose counters that require multiple passes?

*RESOLVED* Yes - users should re-submit a command buffer with the same
commands in it multiple times, specifying the pass to count as the query
parameter in VkPerformanceQuerySubmitInfoKHR.

4) How to handle counters across parallel workloads?

*RESOLVED* In the spirit of Vulkan, a counter description flag
ename:VK_PERFORMANCE_COUNTER_DESCRIPTION_CONCURRENTLY_IMPACTED_BIT_KHR
denotes that the accuracy of a counter result is affected by parallel
workloads.

5) How to handle secondary command buffers?

*RESOLVED* Secondary command buffers inherit any counter pass index
specified in the parent primary command buffer.
Note: this is no longer an issue after change from issue 10 resolution

6) What commands does the profiling lock have to be held for?

*RESOLVED* For any command buffer that is being queried with a performance
query pool, the profiling lock must: be held while that command buffer is in
the _recording_, _executable_, or _pending state_.

7) Should we support flink:vkCmdCopyQueryPoolResults?

*RESOLVED* Yes.

8) Should we allow performance queries to interact with multiview?

*RESOLVED* Yes, but the performance queries must be performed once for each
pass per view.

9) Should a `queryCount > 1` be usable for performance queries?

*RESOLVED* Yes.
Some vendors will have costly performance counter query pool creation, and
would rather if a certain set of counters were to be used multiple times
that a `queryCount > 1` can be used to amortize the instantiation cost.

10) Should we introduce an indirect mechanism to set the counter pass index?

*RESOLVED* Specify the counter pass index at submit time instead, to avoid
requiring re-recording of command buffers when multiple counter passes are
needed.


=== Examples

The following example shows how to find what performance counters a queue
family supports, setup a query pool to record these performance counters,
how to add the query pool to the command buffer to record information, and
how to get the results from the query pool.

[source,c++]
--------------------------------------
// A previously created physical device
VkPhysicalDevice physicalDevice;

// One of the queue families our device supports
uint32_t queueFamilyIndex;

uint32_t counterCount;

// Get the count of counters supported
vkEnumeratePhysicalDeviceQueueFamilyPerformanceQueryCountersKHR(
  physicalDevice,
  queueFamilyIndex,
  &counterCount,
  NULL,
  NULL);

VkPerformanceCounterKHR* counters =
  malloc(sizeof(VkPerformanceCounterKHR) * counterCount);
VkPerformanceCounterDescriptionKHR* counterDescriptions =
  malloc(sizeof(VkPerformanceCounterDescriptionKHR) * counterCount);

// Get the counters supported
vkEnumeratePhysicalDeviceQueueFamilyPerformanceQueryCountersKHR(
  physicalDevice,
  queueFamilyIndex,
  &counterCount,
  counters,
  counterDescriptions);

// Try to enable the first 8 counters
uint32_t enabledCounters[8];

const uint32_t enabledCounterCount = min(counterCount, 8));

for (uint32_t i = 0; i < enabledCounterCount; i++) {
  enabledCounters[i] = i;
}

// A previously created device that had the performanceCounterQueryPools feature
// set to VK_TRUE
VkDevice device;

VkQueryPoolPerformanceCreateInfoKHR performanceQueryCreateInfo = {
  VK_STRUCTURE_TYPE_QUERY_POOL_PERFORMANCE_CREATE_INFO_KHR,
  NULL,

  // Specify the queue family that this performance query is performed on
  queueFamilyIndex,

  // The number of counters to enable
  enabledCounterCount,

  // The array of indices of counters to enable
  enabledCounters
};


// Get the number of passes our counters will require.
uint32_t numPasses;

vkGetPhysicalDeviceQueueFamilyPerformanceQueryPassesKHR(
  physicalDevice,
  &performanceQueryCreateInfo,
  &numPasses);

VkQueryPoolCreateInfo queryPoolCreateInfo = {
  VK_STRUCTURE_TYPE_QUERY_POOL_CREATE_INFO,
  &performanceQueryCreateInfo,
  0,

  // Using our new query type here
  VK_QUERY_TYPE_PERFORMANCE_QUERY_KHR,

  1,

  0
};

VkQueryPool queryPool;

VkResult result = vkCreateQueryPool(
  device,
  &queryPoolCreateInfo,
  NULL,
  &queryPool);

assert(VK_SUCCESS == result);

// A queue from queueFamilyIndex
VkQueue queue;

// A command buffer we want to record counters on
VkCommandBuffer commandBuffer;

VkCommandBufferBeginInfo commandBufferBeginInfo = {
  VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO,
  NULL,
  0,
  NULL
};

VkAcquireProfilingLockInfoKHR lockInfo = {
  VK_STRUCTURE_TYPE_ACQUIRE_PROFILING_LOCK_INFO_KHR,
  NULL,
  0,
  UINT64_MAX // Wait forever for the lock
};

// Acquire the profiling lock before we record command buffers
// that will use performance queries

result = vkAcquireProfilingLockKHR(device, &lockInfo);

assert(VK_SUCCESS == result);

result = vkBeginCommandBuffer(commandBuffer, &commandBufferBeginInfo);

assert(VK_SUCCESS == result);

vkCmdResetQueryPool(
  commandBuffer,
  queryPool,
  0,
  1);

vkCmdBeginQuery(
  commandBuffer,
  queryPool,
  0,
  0);

// Perform the commands you want to get performance information on
// ...

// Perform a barrier to ensure all previous commands were complete before
// ending the query
vkCmdPipelineBarrier(commandBuffer,
  VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
  VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
  0,
  0,
  NULL,
  0,
  NULL,
  0,
  NULL);

vkCmdEndQuery(
  commandBuffer,
  queryPool,
  0);

result = vkEndCommandBuffer(commandBuffer);

assert(VK_SUCCESS == result);

for (uint32_t counterPass = 0; counterPass < numPasses; counterPass++) {

  VkPerformanceQuerySubmitInfoKHR performanceQuerySubmitInfo = {
    VK_STRUCTURE_TYPE_PERFORMANCE_QUERY_SUBMIT_INFO_KHR,
    NULL,
    counterPass
  };


  // Submit the command buffer and wait for its completion
  // ...
}

// Release the profiling lock after the command buffer is no longer in the
// pending state.
vkReleaseProfilingLockKHR(device);

result = vkResetCommandBuffer(commandBuffer, 0);

assert(VK_SUCCESS == result);

// Create an array to hold the results of all counters
VkPerformanceCounterResultKHR* recordedCounters = malloc(
  sizeof(VkPerformanceCounterResultKHR) * enabledCounterCount);

result = vkGetQueryPoolResults(
  device,
  queryPool,
  0,
  1,
  sizeof(VkPerformanceCounterResultKHR) * enabledCounterCount,
  recordedCounters,
  sizeof(VkPerformanceCounterResultKHR),
  NULL);

// recordedCounters is filled with our counters, we will look at one for posterity
switch (counters[0].storage) {
  case VK_PERFORMANCE_COUNTER_STORAGE_INT32:
    // use recordCounters[0].int32 to get at the counter result!
    break;
  case VK_PERFORMANCE_COUNTER_STORAGE_INT64:
    // use recordCounters[0].int64 to get at the counter result!
    break;
  case VK_PERFORMANCE_COUNTER_STORAGE_UINT32:
    // use recordCounters[0].uint32 to get at the counter result!
    break;
  case VK_PERFORMANCE_COUNTER_STORAGE_UINT64:
    // use recordCounters[0].uint64 to get at the counter result!
    break;
  case VK_PERFORMANCE_COUNTER_STORAGE_FLOAT32:
    // use recordCounters[0].float32 to get at the counter result!
    break;
  case VK_PERFORMANCE_COUNTER_STORAGE_FLOAT64:
    // use recordCounters[0].float64 to get at the counter result!
    break;
}
--------------------------------------

=== Version History

 * Revision 1, 2019-10-08