Buffered services#
For the buffered approach, supported buffer record categories are enumerated in rocprofiler_buffer_category_t category field.
Overview#
In buffered approach, callbacks are receieved for batches of records from an internal (background) thread.
Supported buffered tracing services are enumerated in rocprofiler_buffer_tracing_kind_t. Configuring
a buffer tracing service requires the creation of a buffer. When the buffer is “flushed”, either implicitly
or explicitly, a callback to the tool will be invoked which provides an array of one or more buffer records.
A buffer can be explicitly flushed via the rocprofiler_flush_buffer function.
Subscribing to Buffer Tracing Services#
During tool initialization, tools configure callback tracing via the rocprofiler_configure_buffer_tracing_service
function. However, before invoking rocprofiler_configure_buffer_tracing_service, the tool must create a buffer
for the tracing records.
Creating a Buffer#
rocprofiler_status_t
rocprofiler_create_buffer(rocprofiler_context_id_t context,
size_t size,
size_t watermark,
rocprofiler_buffer_policy_t policy,
rocprofiler_buffer_tracing_cb_t callback,
void* callback_data,
rocprofiler_buffer_id_t* buffer_id);
The size parameter is the size of the buffer in bytes and will be rounded up to the nearest
memory page size (defined by sysconf(_SC_PAGESIZE)); the default memory page size on Linux
is 4096 bytes (4 KB).
The watermark parameter specifies the number of bytes at which
the buffer should be “flushed”, i.e. when the records in the buffer should invoke the
callback parameter to deliver the records to the tool. For example, if a buffer has a size
of 4096 bytes and the watermark is set to 48 bytes, six 8-byte records can be placed in the
buffer before callback is invoked. However, every 64-byte record that is placed in the
buffer will trigger a flush. It is safe to set the watermark to any value between
zero and the buffer size.
The policy parameter specifies the behavior for when a record is larger than the
amount of free space in the current buffer. For example, if a buffer has a size of
4000 bytes with a watermark set to 4000 bytes and 3998 of the bytes in the buffer
have been populated with records, the policy dictates how to handle an incoming record >
2 bytes. The ROCPROFILER_BUFFER_POLICY_DISCARD policy dictates that all records greater
than should 2 bytes should be dropped until the tool explicitly flushes the buffer via
a rocprofiler_flush_buffer function call whereas the ROCPROFILER_BUFFER_POLICY_LOSSLESS
policy dictates that the current buffer should be swapped out for an empty buffer and placed
in that new buffer and former (full) buffer should be implicitly flushed.
The callback parameter is the function that rocprofiler-sdk should invoke when flushing
the buffer; the value of the callback_data parameter will be passed as one of the arguments
to the callback function.
The buffer_id parameter is an output parameter for the function call and will have a
non-zero handle field after successful buffer creation.
Creating a Dedicated Thread for Buffer Callbacks#
By default, all buffers will use the same (default) background thread created by rocprofiler-sdk to invoke their callback. However, rocprofiler-sdk provides an interface for tools to specify the creation of an additional background thread for one or more of their buffers.
Callback threads for buffers are created via the rocprofiler_create_callback_thread function:
rocprofiler_status_t
rocprofiler_create_callback_thread(rocprofiler_callback_thread_t* cb_thread_id);
Buffers are assigned to that callback thread via the rocprofiler_assign_callback_thread function:
rocprofiler_status_t
rocprofiler_assign_callback_thread(rocprofiler_buffer_id_t buffer_id,
rocprofiler_callback_thread_t cb_thread_id);
Buffer Callback Thread Creation and Assignment Example#
{
// create a context
auto context_id = rocprofiler_context_id_t{};
rocprofiler_create_context(&context_id);
// create a buffer associated with the context
auto buffer_id = rocprofiler_buffer_id_t{};
rocprofiler_create_buffer(context_id, ..., &buffer_id);
// specify that a new callback thread should be created and provide
// and assign the identifier for it to the "thr_id" variable
auto thr_id = rocprofiler_callback_thread_t{};
rocprofiler_create_callback_thread(&thr_id);
// assign the buffer callback to be delivered on this thread
rocprofiler_assign_callback_thread(buffer_id, thr_id);
}
Configuring Buffer Tracing Services#
rocprofiler_status_t
rocprofiler_configure_buffer_tracing_service(rocprofiler_context_id_t context_id,
rocprofiler_buffer_tracing_kind_t kind,
rocprofiler_tracing_operation_t* operations,
size_t operations_count,
rocprofiler_buffer_id_t buffer_id);
The kind parameter is a high-level specifier of which service to trace (also known as a “domain”).
Domain examples include, but are not limited to, the HIP API, the HSA API, and kernel dispatches.
For each domain, there are (often) various “operations”, which can be used to restrict the callbacks
to a subset within the domain. For domains which correspond to APIs, the “operations” are the functions
which compose the API. If all operations in a domain should be traced, the operations and operations_count
parameters can be set to nullptr and 0, respectively. If the tracing domain should be restricted to a subset
of operations, the tool library should specify a C-array of type rocprofiler_tracing_operation_t and the
size of the array for the operations and operations_count parameter.
Similar to rocprofiler_configure_callback_tracing_service,
rocprofiler_configure_buffer_tracing_service will return an error if a buffer service for given context
and given domain is configured more than once.
Example#
{
auto ctx = rocprofiler_context_id_t{};
// ... creation of context, etc. ...
// buffer parameters
constexpr auto KB = 1024; // 1024 bytes
constexpr auto buffer_size = 16 * KB;
constexpr auto watermark = 15 * KB;
constexpr auto policy = ROCPROFILER_BUFFER_POLICY_LOSSLESS;
// buffer handle
auto buffer_id = rocprofiler_buffer_id_t{};
// create a buffer associated with the context
rocprofiler_create_buffer(
context_id, buffer_size, watermark, policy, callback_func, nullptr, &buffer_id);
// configure HIP runtime API function records to be placed in buffer
rocprofiler_configure_buffer_tracing_service(
ctx, ROCPROFILER_BUFFER_TRACING_HIP_RUNTIME_API, nullptr, 0, buffer_id);
// configure kernel dispatch records to be placed in buffer
// (more than one service can use the same buffer)
rocprofiler_configure_buffer_tracing_service(
ctx, ROCPROFILER_BUFFER_TRACING_KERNEL_DISPATCH, nullptr, 0, buffer_id);
// ... etc. ...
}
Buffer Tracing Callback Function#
Rocprofiler-sdk buffer tracing callback functions have the signature:
typedef void (*rocprofiler_buffer_tracing_cb_t)(rocprofiler_context_id_t context,
rocprofiler_buffer_id_t buffer_id,
rocprofiler_record_header_t** headers,
size_t num_headers,
void* data,
uint64_t drop_count);
The rocprofiler_record_header_t data type provides three pieces of information:
Category (
rocprofiler_buffer_category_t)Kind
Payload
The category is used to distinguish the classification of the buffer record. For all
services configured via rocprofiler_configure_buffer_tracing_service, the category will
be equal to the value of ROCPROFILER_BUFFER_CATEGORY_TRACING. The meaning of the kind
field is dependent on the category but when the category is ROCPROFILER_BUFFER_CATEGORY_TRACING,
the kind value will be equivalent to the is used
to distinguish the rocprofiler_buffer_tracing_kind_t value passed to
rocprofiler_configure_buffer_tracing_service, e.g. ROCPROFILER_BUFFER_TRACING_KERNEL_DISPATCH.
Once the category and kind have been determined, the payload can be casted:
{
if(header->category == ROCPROFILER_BUFFER_CATEGORY_TRACING &&
header->kind == ROCPROFILER_BUFFER_TRACING_HIP_RUNTIME_API)
{
auto* record =
static_cast<rocprofiler_buffer_tracing_hip_api_record_t*>(header->payload);
// ... etc. ...
}
}
Buffer Tracing Callback Function Example#
void
buffer_callback_func(rocprofiler_context_id_t context,
rocprofiler_buffer_id_t buffer_id,
rocprofiler_record_header_t** headers,
size_t num_headers,
void* user_data,
uint64_t drop_count)
{
for(size_t i = 0; i < num_headers; ++i)
{
auto* header = headers[i];
if(header->category == ROCPROFILER_BUFFER_CATEGORY_TRACING &&
header->kind == ROCPROFILER_BUFFER_TRACING_HIP_RUNTIME_API)
{
auto* record =
static_cast<rocprofiler_buffer_tracing_hip_api_record_t*>(header->payload);
// ... etc. ...
}
else if(header->category == ROCPROFILER_BUFFER_CATEGORY_TRACING &&
header->kind == ROCPROFILER_BUFFER_TRACING_KERNEL_DISPATCH)
{
auto* record =
static_cast<rocprofiler_buffer_tracing_kernel_dispatch_record_t*>(header->payload);
// ... etc. ...
}
else
{
throw std::runtime_error{"unhandled record header category + kind"};
}
}
}
Buffer Tracing Record#
Unlike callback tracing records, there is no common set of data for each buffer tracing record. However,
many buffer tracing records contain a kind field and an operation field.
The name of a tracing kind can be obtained via the rocprofiler_query_buffer_tracing_kind_name function.
The name of an operation specific to a tracing kind can be obtained via the rocprofiler_query_buffer_tracing_kind_operation_name
function. One can also iterate over all the buffer tracing kinds and operations for each tracing kind via the
rocprofiler_iterate_buffer_tracing_kinds and rocprofiler_iterate_buffer_tracing_kind_operations functions.
The buffer tracing record data types can be found in the rocprofiler-sdk/buffer_tracing.h header
(source/include/rocprofiler-sdk/buffer_tracing.h in the rocprofiler-sdk GitHub repository).