Trace and Replay Tools

The LunarG Vulkan SDK includes application trace, replay, and validation programs and libraries.

Tracing and Trace Files

The LunarG Vulkan SDK provides the capability to trace Vulkan applications. The SDK includes executables and libraries to trace both local and remote apps.

When tracing, the tools record the application's Vulkan API calls to a file named with a .vktrace suffix. The call information is stored in the trace file in a compact binary format.

The trace program is named vktrace. Options to the vktrace command include:

Trace Option Description Default
-a <string>
‑‑Arguments <string>
Command line arguments to pass to the application to be traced none
-o <string>
‑‑OutputTrace <string>
Name of the generated trace file vktrace_out.vktrace
-p <string>
‑‑Program <string>
Name of the application to trace if not provided, server mode tracing is enabled
-ptm <bool>
‑‑PrintTraceMessages <bool>
Print trace messages to console on
-s <string>
‑‑Screenshot <string>
Comma-separated list of frame numbers of which to take screen shots no screenshots
-w <string>
‑‑WorkingDir <string>
Alternate working directory the application's directory
-P <bool>
‑‑PMB <bool>
Optimize trace of persistently mapped buffers true
-tr <string>
‑‑TraceTrigger <string>
Start/stop trim by hotkey or frame range.
String arg is one of:
    hotkey-[F1-F12
TAB
-v <string>
‑‑Verbosity <string>
Verbosity mode - "quiet", "errors", "warnings", or "full" errors

In local tracing mode, both the vktrace and application executables reside on the same system.

An example command to trace the SDK sample cube application in local mode follows.

Linux shell:

$ cd examples/build
$ vktrace -p ./cube -o cubetrace.vktrace

Windows Powershell:

PS> cd C:\Users\<Name>\Desktop
PS> vktrace -p C:\VulkanSDK\<Version>\Bin\cube.exe -o cubetrace.vktrace

Note: Subsequent command examples in this document are written using Linux shell commands. These example commands can be translated and used as Windows Powershell commands.

Trace packets are written to the file cubetrace.vktrace in the local directory. Output messages from the replay operation are written to stdout.

Important: Subsequent vktrace runs with the same -o option value will overwrite the trace file, preventing the generation of multiple, large trace files. Be sure to specify a unique output trace file name for each vktrace invocation if you do not desire this behaviour.

Client/Server Mode

The tools also support tracing Vulkan applications in client/server mode, where the trace server resides on a local or a remote system.

Server

In client/server mode, the vktrace server is started without specifying the -p or --Program option. Invoked in this fashion, vktrace enters a waiting mode for trace packets.

$ mkdir examples/traces
$ cd examples/traces
$ vktrace -o cubetrace_s.vktrace
No program (-p) parameter found: Running vktrace as server.

The trace file will be written to cubetrace_s.vktrace. If additional programs are traced with this trace server, subsequent trace files will be named cubetrace_s-<N>.vktrace, with the trace server incrementing N for each time the application is run.

Client

The tracer is implemented as a Vulkan layer. When tracing in server mode, the local or remote client must enable the Vktrace layer. The Vktrace layer must be the first layer identified in the VK_INSTANCE_LAYERS lists.

$ export VK_INSTANCE_LAYERS=VK_LAYER_LUNARG_vktrace

Local Client

Local client/server mode is particularly useful for Vulkan applications with multiple runtime options or complicated startup.

In local client/server mode, the tracer layer must be enabled before the local client application to be traced is launched.

$ cd examples/build
$ export VK_INSTANCE_LAYERS=VK_LAYER_LUNARG_vktrace
$ ./cube

The generated trace file is found at examples/traces/cubetrace_s.vktrace.

Note: The cube application is used to demonstrate tracing in client/server mode. cube is a very simple application, and would not be traced in this mode in practice.

Remote Client

Remote client/server mode is useful if the client is a mobile device or running in a lightweight environment that might not have the disk or other capabilities to store large trace files.

In remote client/server mode, the remote client must additionally identify the IP address of the trace server system.

$ cd examples/build
$ export VKTRACE_LIB_IPADDR=<ip address of trace server system>
$ export VK_INSTANCE_LAYERS=Vktrace
$ ./cube

The generated trace file is located at examples/traces/cubetrace_s.vktrace on the remote trace server system.

Replay

The LunarG Vulkan SDK provides the capability to replay a Vulkan application trace.

Important: Trace files generated with earlier versions of the vktrace tools may not be replayable with later versions of the tools. The trace file format has evolved over time - vkreplay attempts to identify incompatible versions during replay and can often successfully replay them, but it does not handle all such cases.

Important: Trace files generated on one GPU may or may not be replayable on other GPUs, as well as trace files generated on different OSes and different driver versions. vkreplay attempts to replay such trace files, translating API calls as needed for the new platform, but it does not handle all such cases.

The trace replay program is vkreplay. vkreplay options include:

Replay Option Description Default
-o <string>
‑‑Open <string>
Name of trace file to open and replay required
-l <int>
‑‑NumLoops <int>
Number of times to replay the trace file 1
-lsf <int>
‑‑LoopStartFrame <int>
The start frame number of the loop range 0
-lef <int>
‑‑LoopEndFrame <int>
The end frame number of the loop range the last frame in the tracefile
-s <string>
‑‑Screenshot <string>
Comma-separated list of frame numbers of which to take screen shots no screenshots
-sf <string>
‑‑ScreenshotFormat <string>
Color Space format of screenshot files. Formats are UNORM, SNORM, USCALED, SSCALED, UINT, SINT, SRGB Format of swapchain image
-v <string>
‑‑Verbosity <string>
Verbosity mode - "quiet", "errors", "warnings", or "full" errors

To replay the cube application trace first captured in the example above:

$ cd examples/build
$ vkreplay -o cubetrace.vktrace -l 5

If the trace is rather short, the replay may finish quickly. Specify the -l or --NumLoops option to replay the trace NumLoops option value times.

Output messages from the replay operation are written to stdout.

Replayer Interaction with Layers

The Vulkan validation layers may be enabled for trace replay. Replaying a trace with layers activated provides many benefits. Developers can take advantage of new validation capabilities as they are developed with older and existing trace files.

To activate specific layers on a trace replay, set the VK_INSTANCE_LAYERS environment variable to a colon-separated list of layer names before replaying the trace. Refer to the Vulkan Validation and Debugging Layers guide for additional information on layers and how to configure layer output options.

vktraceviewer

The Vulkan SDK includes vktraceviewer. This tool allows interactive creation and viewing of Vulkan trace files. In the future, it will include support for interactively playing back trace files. This is alpha software.

In order to run vktraceviewer on Linux, Qt5 libraries need to be installed on the system.

Persistently Mapped Buffers and vktrace

If a Vulkan program uses persistently mapped buffers (PMB) that are allocated via vkMapMemory, vktrace can track changes to PMB and automatically copy modified PMB pages to the trace file, rather than requiring that the Vulkan program call vkFlushMappedMemoryRanges to specify what PMB buffers should be copied. On Windows, the trace layer detects changes to PMB pages by setting the PAGE_GUARD flag for mapped memory pages and installing an exception handler for PAGE_GUARD that keeps track of which pages have been modified. On Linux, the trace layer detects changes to PMB pages by examining /proc/self/pagemap.

Tracking of changes to PMB using the above techniques is enabled by default. If you wish to disable PMB tracking, it can be disabled by with the --PMB false option to the vktrace command. Disabling PMB tracking can result in some mapped memory changes not being detected by the trace layer, a larger trace file, and/or slower trace/replay.

Trace Tools Enviroment Variables

Several enviroment variables can be set to change the behavior of vktrace/vkrepay: