NVIDIA GPUDirect Storage Best Practices Guide
NVIDIA GPUDirect Storage Best Practices Guide
The Best Practices guide provides guidance from experts who are knowledgeable about NVIDIA® GPUDirect® Storage (GDS).
The purpose of the Best Practices guide is to provide guidance from experts who are knowledgeable about NVIDIA® GPUDirect® Storage (GDS). This guide also provides information about the lessons learned when building and massively scaling GPU accelerated I/O storage infrastructures. The intended audience includes data center planning staff, system builders, developers, and storage vendors.
This section describes the settings required for GDS.
For the best performance, multiple software settings are required across the entire system, and some settings are specific to the filesystem that you are using.
For more information, refer to the GPUDirect Storage Installation and Troubleshooting Guide.
2.1. System Settings
For GDS p2p support on Grace CPU based DGX (Grace Hopper) platform, IOMMU should be enabled and passthrough settings should be disabled.
The following are system settings that we recommend for the best performance on a bare metal x86_64 based platform.
- PCIe Access Control Services (ACS).
ACS forces P2P PCIe transactions to go up through the PCIe Root Complex, which does not enable GDS to bypass the CPU on paths between a network adapter or NVMe and the GPU in systems that include a PCIe switch.
For the optimal GDS performance, disable ACS.
To list all of the PCI switches that have ACS enabled, issue /usr/local/cuda/gds/tools/gdscheck -p
.
- NIC versions
- When using Mellanox ConnectX-5 or later, the HCAs must be configured in InfiniBand or RoCE v2 mode.
- For GDS support, MLNX_OFED 5.4 or later is required.
2.2. Use of CUDA Context in GPU Kernels and Storage IO
There are scenarios where the GDS workload data can be posted through intermediate buffers called bounce buffers. Hence a D2D copy is involved to/from these GPU bounce buffers to/from the application's GPU buffers. The cuFile library posts these IOs on a stream created on the primary context. If a heavy compute job or application kernel is running in the background in the form of GPU kernels on a separate context (not the primary context), it can interfere with the D2D copies and increase the D2D copy launch times. This problem does not happen if the compute kernels are running in the primary context, so it is recommended that the application should launch the GPU kernels on the primary context instead of using a separate context.
If the application uses CUDA runtime API, the kernel launches by default would happen in the primary context.
2.3. cuFile Configuration Settings
The cuFile configuration settings in GDS are stored in the /etc/cufile.json file.
You can edit the file for best performance for your application as shown below. Refer to https://docs.nvidia.com/gpudirect-storage/configuration-guide/index.html#gds-parameters. To display the configuration setting, run the following command:
$cat /etc/cufile.json
A portion of the sample output:
"properties": {
// max IO size issued by cuFile to nvidia-fs driver (in KB)
"max_direct_io_size_kb" : 16384,
...
}
For the requested IO size, GDS issues IO requests sequentially in chunks of reads/writes based on the max_direct_io_size
parameter. Larger values of max_direct_io_size
will result in a reduced number of calls to the IO stack and might result in higher throughput.
The max_direct_io_size_kb
parameter can be set to a value that is a multiple of 64K. This process defines the additional system memory that is used for each buffer during cuFileBufRegister
up to a maximum value that is defined by the properties:max_direct_io_size_kb
parameter. The maximum direct IO size that GDS can handle is 16MB, and this value can be reduced to 1MB to reduce the amount of system memory that is used per buffer.
The total system memory that is used can be obtained from nvidia-fs
stats.
In this example, each of 256 threads register a 1MB buffer for GDS.
- Run the following command:
$ cat /proc/driver/nvidia-fs/stats
- Review the output:
NVFS statistics(ver:1.0) Active Shadow-Buffer (MB): 256...
There are many tunables available in cufile.json
. Refer to GPUDirect Storage Parameters.
This section describes best practices to remember when you use the GDS APIs.
The cuFile APIs are designed to be thread safe.
The fork system call should not be used after the library is initialized. The behavior of the APIs after the fork system call is undefined in the child process.
The APIs with GPU buffers should be called in a valid CUDA context.
The following table outlines recommendations for various I/O specific use cases and their corresponding cuFile APIs which would be best suited.Mode | IO Behavior | Use Case | Pros/Cons |
---|---|---|---|
|
Synchronous submission Synchronous completion |
Single-threaded application using standard file system calls for single large file and large buffers (>16MB) | Pros
Cons
|
cuFile Threadpool enabled
|
Synchronous submission Synchronous completion |
|
Pros
Cons
|
|
Synchronous submission Asynchronous completion |
|
Pros
Cons
|
|
Asynchronous submission Asynchronous completion |
|
Pros
Cons
|
3.1. cuFileDriverOpen
The cuFileDriverOpen
API should be invoked only once per process and before you invoke any other cuFile API. The application should call this API to avoid the latency of the driver that will be otherwise incurred in the first IO call.
3.2. cuFileHandleRegister
The cuFileHandleRegister
API converts a file descriptor to a cuFileHandle
and checks the ability of the named file, at its mount point, to be supported via GDS on this platform. Required.
There should be one handle for each file descriptor.
The same handle can be shared by multiple threads. Refer to the sample programs for more information about using the same handle by multiple threads.
In the compatibility mode, an additional fd
can be opened without requiring the O_DIRECT
mode. This mode can also handle unaligned reads/writes, even when POSIX cannot.
3.3. cuFileBufRegister, cuFileRead, cuFileWrite, cuFileBatchIOSubmit, cuFileBatchIOGetStatus, cuFileReadAsync, cuFileWriteAsync, and cuFileStreamRegister
GPU buffers need to be exposed to third-party devices to enable DMA by those devices. The set of pages that span those buffers in the GPU virtual address space need to be mapped to the Base Address Register (BAR) space, and this mapping is an overhead.
The process to accomplish this mapping is called registration.
Explicit GPU buffer registration with the cuFileBufRegister
API is optional. If the user buffer is not registered, an intermediate pre-registered GPU buffer that is owned by the cuFile implementation is used, and there is an extra copy from there to the user buffer. The following table provides guidance on whether registration is profitable.
IO Pattern 1 is a suboptimal baseline case and is not referenced in this table.
Use Case | Description | Recommendation |
---|---|---|
A 4KB-aligned GPU buffer is reused as an intermediate buffer to read or write data by using optimal IO sizes for storage systems in multiples of 4KB. | The GPU buffer is used as an intermediate buffer to stream the contents or to populate a different data structure in GPU memory. You can implement this use case for IO libraries with DSG. |
Register this reusable intermediate buffer to avoid the additional internal staging of data by using GPU bounce buffers in the cuFile library. See IO Pattern 2 for the recommended usage. |
Filling a large GPU buffer for one use. | The GPU buffer is the final location of the data. Since the buffer will not be reused, the registration cost will not be amortized. A usage example is reading large preformatted checkpoint binary data. Registering a large buffer can have a latency impact when the buffer is registered. |
This can also cause BAR memory exhaustion because running multiple threads or applications will compete for BAR memory. Read or write the data without buffer registration. See IO Pattern 3 for the recommended usage. |
Partitioning a GPU buffer to be accessed across multiple threads. | The main thread allocates a large chunk of memory and creates multiple threads. Each thread registers a portion of the memory chunk independently and uses that as in IO Pattern 2. You can also register the entire memory in the parent thread and use this registered buffer with the size and |
Allocate, register, and deregister the buffers in each thread independently for simple IO workflows. For cases where the GPU memory is preallocated, each thread can set the appropriate context and register the buffers independently. See IO Pattern 6 for the recommended usage. After you install the GDS package, see |
GPU offsets, file offsets, and IO request sizes are unaligned. | The IO reads or writes are mostly unaligned. An intermediate aligned buffer might be needed to handle alignment issues with GPU offsets, file offsets, and IO sizes. | Do not register the buffer. See IO Pattern 4 and IO Pattern 5. |
Working on a GPU with a small BAR space as compared to the available GPU memory. | In some GPU SKUs, the BAR memory is smaller than the total device memory. | To avoid failures because of BAR memory exhaustion, do not register the buffer. See IO Pattern 3. |
3.3.1. IO Pattern 1
The following is a code sample for IO Pattern 1.
1 #define MB(x) ((x)*1024*1024L)
2 #define GB(x) ((x)*1024*1024L*1024L)
3
4
5 void thread_func(CUfileHandle_t cuHandle)
6 {
7 void *devPtr_base;
8 int readSize = MB(100);
9 int devPtr_offset = 0;
10 int file_offset = 0;
11 int ret = 0;
12
13
14 cudaSetDevice(0);
15 cudaMalloc(&devPtr_base, GB(1));
16
17 for (int i = 0; i < 10; i++) {
18
19 cuFileBufRegister((char *)devPtr_base + devPtr_offset, readSize, 0);
20
21 ret = cuFileRead(cuHandle, (char *)devPtr_base + devPtr_offset,
readSize, file_offset, 0);
22
23
<... launch cuda kernel using contents at devPtr_base + devPtr_offset … >
24 file_offset += readSize;
25 devPtr_offset += readSize;
26
27 cuFileBufDeregister((char *)devPtr_base + devPtr_offset);
28 }
29 }
- Allocate 1 GB of GPU memory by using cudaMalloc.
- Fill the 1 GB by reading 100 MB at a time from file as seen in the following loop:
- At line 19, the GPU buffer of 100 MB is registered.
- Submit the read for 100MB (readsize is 100 MB).
- At line 27, the GPU buffer of 100 MB is deregistered.
Although semantically correct, this loop might not provide the best performance becausecuFileBufRegister
and cuFileBufDeregister
are continuously issued in the loop. For example, this problem can be addressed as shown in IO-Pattern - 2.
3.3.2. IO Pattern 2
The following is a code sample for IO Pattern 2.
1 #define MB(x) ((x)*1024*1024L)
2 #define GB(x) ((x)*1024*1024L*1024L)
3
4
5 void thread_func(CUfileHandle_t cuHandle)
6 {
7 void *devPtr_base;
8 int readSize = MB(100);
9 int devPtr_offset = 0;
10 int file_offset = 0;
11 int ret = 0;
12
13
14 cudaSetDevice(0);
15 cudaMalloc(&devPtr_base, GB(1));
16 cuFileBufRegister(devPtr_base, GB(1), 0);
17
18 for (int i = 0; i < 10; i++) {
19
20 ret = cuFileRead(cuHandle, devPtr_base,
readSize, file_offset, devPtr_offset);
21
22 <... launch cuda kernel using contents at devPtr_base + devPtr_offset … >
23
24 file_offset += readSize;
25 devPtr_offset += readSize;
27
28 }
29 cuFileBufDeregister(devPtr_base);
30 }
3.3.3. IO Pattern 3
The following is a code sample for IO Pattern 3.
1 #define MB(x) ((x)*1024*1024L)
2 #define GB(x) ((x)*1024*1024L*1024L)
3
4
5 void thread_func(CUfileHandle_t cuHandle)
6 {
7 void *devPtr_base;
8 int readSize = MB(100);
9 int devPtr_offset = 0;
10 int file_offset = 0;
11 int ret = 0;
12
13 cudaSetDevice(0);
14 cudaMalloc(&devPtr_base, GB(1));
15
16 for (int i = 0; i < 10; i++) {
17
18 ret = cuFileRead(cuHandle, (char *)devPtr_base,
readSize, file_offset, devPtr_offset);
19
20 <... launch cuda kernel using contents at devPtr_base + devPtr_offset … >
21
22 file_offset += readSize;
23 devPtr_offset += readSize;
24 }
25 }
This example demonstrates the usage of cuFileRead
/cuFileWrite
APIs without using the cuFileBufRegister
and cuFileBufDeRegister
APIs. The IO-Pattern - 3 code snippet is the same as the IO-Pattern-1 and IO-Pattern-2 code snippets but the cuFileBufRegister
API is not used.
- Allocate 1 GB of GPU memory.
- Fill the entire GPU memory of 1 GB by reading 100 MB at a time from file as seen in the loop.
Although semantically correct, this loop might not be optimal.
Internally, GDS uses GPU bounce buffers to perform IOs. Bounce buffers are GPU memory allocations that are internal to GDS, and these buffers are registered and managed by the GDS library. The number of bounce buffers is capped based on the max_device_cache_size
(representing the total size of the bounce buffer cache) and per_buffer_cache_size
(representing the size of each buffer) setting in the /etc/cufile.json
file. The default value for max_device_cache_size
and per_buffer_cache_size
are 128MB and 1MB respectively, which amounts to 128 bounce buffers in total by default.
3.3.4. IO Pattern 4
The following is a code sample for IO Pattern 4. This is an unaligned IO due to file offset being unaligned.
1 #define MB(x) ((x)*1024*1024L)
2 #define GB(x) ((x)*1024*1024L*1024L)
3
4
5 void thread_func(CUfileHandle_t cuHandle)
6 {
7 void *devPtr_base;
8 int readSize = MB(100);
9 int devPtr_offset = 0;
10 int file_offset = 3; // Start from odd offset
11 int ret = 0;
12
13
14 cudaSetDevice(0);
15 cudaMalloc(&devPtr_base, GB(1));
16 cuFileBufRegister(devPtr_base, GB(1), 0);
17
18 for (int i = 0; i < 10; i++) {
19 // IO issued at offsets which are not 4K aligned
20 ret = cuFileRead(cuHandle, devPtr_base,
readSize, file_offset, devPtr_offset);
21 assert(ret >= 0);
<... launch cuda kernel using contents at devPtr_base + devPtr_offset … >
23
24 file_offset += readSize;
25 devPtr_offset += readSize;
27
28 }
cuFileBufDeRegister(devPtr_base);
29 }
This example demonstrates the usage of cuFileRead
/cuFileWrite
when IO is unaligned.
An IO is unaligned if one of the following conditions is true:
- The
file_offset
that was issued incuFileRead
/cuFileWrite
is not 4K aligned. - The size that was issued in
cuFileRead
/cuFileWrite
is not 4K aligned. - The
devPtr_base
that was issued incuFileRead
/cuFileWrite
is not 4K aligned. - The
devPtr_offset
that was issued incuFileRead
/cuFileWrite
is not 4K aligned.
In the above example, the initialization of file_offset
is on line 10.
- After allocating 1 GB of GPU memory,
cuFileBufRegister
is immediately invoked for the entire range of 1 GB as seen on line 16. - Fill the entire 1 GB GPU memory by reading 100 MB at a time from file as seen in the following loop:
- The initial file_offset is at 3, and reads are submitted with a
readSize
value of 100MB at an offset of 3 for each iteration.For example,
file_offset
during each read is not 4K aligned. - Since
file_offset
is not 4K aligned, the GDS library will internally use GPU bounce buffers to complete the IO.The GPU bounce buffer mechanism is identical to IO-Pattern-3.
- The initial file_offset is at 3, and reads are submitted with a
- Unaligned IOs might not be optimal and should be avoided by reading the size value that is specified in multiples of 4KB and the
file_offsets
value that is specified in multiples of 4KB.In the above example, an entire 1GB of GPU memory was registered using
cuFileBufRegister
. However, because the IO was unaligned, GDS library cannot perform IO directly to these registered buffers. To handle unaligned IOs, the library might use GPU bounce buffers to perform the IO and copy the data from the bounce buffers to the application buffers. If the application typically performs unaligned IO, as a best practice, the application buffers do not need to be registered with the GDS library.The example in IO Pattern 4 demonstrates what happens when
file_offset
is unaligned; the previously mentioned points are accurate if either of the unaligned conditions is true.
If the applications cannot issue 4K aligned IO, instead of using the cuFileBufRegister
API, use the cuFileRead
/cuFileWrite
APIs as described in IO-Pattern-2.
Remember the following information:
- When the write workload is unaligned, GDS uses Read-Modify-Write internally using POSIX mode.
3.3.5. IO Pattern 5
The following is a code sample for IO Pattern 5. This IO is an unaligned IO due to buffer pointer and offset not being 4K aligned.
1 #define MB(x) ((x)*1024*1024L)
2 #define GB(x) ((x)*1024*1024L*1024L)
3
4
5 void thread_func(CUfileHandle_t cuHandle)
6 {
7 void *devPtr_base;
8 int readSize = MB(100);
9 int devPtr_offset = 3; // Start from odd offset
10 int file_offset = 0;
11 int ret = 0;
12
13
14 cudaSetDevice(0);
15 cudaMalloc(&devPtr_base, GB(1));
16 cuFileBufRegister(devPtr_base, GB(1), 0);
17
18 for (int i = 0; i < 10; i++) {
19 // IO issued at gpu buffer offsets which are not 4K aligned
20 ret = cuFileRead(cuHandle, devPtr_base,
readSize, file_offset, devPtr_offset);
21 assert (ret >= 0);
<... launch cuda kernel using contents at devPtr_base + devPtr_offset … >
23
24 file_offset += readSize;
25 devPtr_offset += readSize;
27
28 }
cuFileBufDeRegister(devPtr_base);
29 }
This example demonstrates using cuFileRead
/cuFileWrite
when IO is unaligned. The devPtr_base + devPtr_offset
that are issued incuFileRead
/cuFileWrite
are not 4K aligned.
If the IO is unaligned, the cuFile library will issue IO through the internal GPU bounce buffer cache. Also, if the allocation of internal cache fails, the IO fails. To avoid IO failure in this case, you can set allow_compat_mode
to true
in the /etc/cufile.json file. With this setting, IO will fallback to the POSIX APIs.
3.3.6. IO Pattern 6
The following program snippets use cuFile batch APIs.
int main(int argc, char *argv[]) {
int fd[MAX_BATCH_IOS];
void *devPtr[MAX_BATCH_IOS];
CUfileDescr_t cf_descr[MAX_BATCH_IOS];
CUfileHandle_t cf_handle[MAX_BATCH_IOS];
CUfileIOParams_t io_batch_params[MAX_BATCH_IOS];
CUfileIOEvents_t io_batch_events[MAX_BATCH_IOS];
<Get program inputs>
status = cuFileDriverOpen();
if (status.err != CU_FILE_SUCCESS) {
std::cerr << "cufile driver open error: "
<< cuFileGetErrorString(status) << std::endl;
return -1;
}
<Open files and call cuFileHandleRegister for each of the batch entry file handles>
<Allocate cuda memory and register buffers using cuFileBufRegister for each of the
batch entries>
for(i = 0; i < batch_size; i++) {
io_batch_params[i].mode = CUFILE_BATCH;
io_batch_params[i].fh = cf_handle[i];
io_batch_params[i].u.batch.devPtr_base = devPtr[i];
io_batch_params[i].u.batch.file_offset = i * size;
io_batch_params[i].u.batch.devPtr_offset = 0;
io_batch_params[i].u.batch.size = size;
io_batch_params[i].opcode = CUFILE_READ;
}
std::cout << "Setting Up Batch" << std::endl;
errorBatch = cuFileBatchIOSetUp(&batch_id, batch_size);
if(errorBatch.err != 0) {
std::cerr << "Error in setting Up Batch" << std::endl;
goto error;
}
errorBatch = cuFileBatchIOSubmit(batch_id, batch_size, io_batch_params, flags);
if(errorBatch.err != 0) {
std::cerr << "Error in IO Batch Submit" << std::endl;
goto error;
}
// Setting min_nr to batch_size for this example.
min_nr = batch_size;
while(num_completed != min_nr) {
memset(io_batch_events, 0, sizeof(*io_batch_events));
nr = batch_size;
errorBatch = cuFileBatchIOGetStatus(batch_id, batch_size, &nr, io_batch_events, NULL);
if(errorBatch.err != 0) {
std::cerr << "Error in IO Batch Get Status" << std::endl;
goto error;
}
std::cout << "Got events " << nr << std::endl;
num_completed += nr;
<Copy to the user buffer>
}
cuFileBatchIODestroy(batch_id);
< Deregister the device memory using cuFileBufDeregister>
status = cuFileDriverClose();
std::cout << "cuFileDriverClose Done" << std::endl;
if (status.err != CU_FILE_SUCCESS) {
…
}
ret = 0;
return ret;
…
}
This program demonstrates a simple use case where cufile batch APIs can be used to perform a READ with a specified batch size. It provides an example of a sequence of calls where each entry uses registered buffers on each individual file descriptor. It may be worthwhile to mention that min_nr
passed to cuFileBatchIOGetStatus()
in the above example was set to batch_size
. It is possible that min_nr
can be set to something less than batch_size
and as the min_nr
number of I/Os are completed, that many numbers of I/Os can be submitted subsequently to the I/O pipeline resulting in an enhanced I/O throughput.
3.3.7. IO Pattern 7
The following program snippets use cuFile stream based async I/O APIs to perform a data integrity test.
typedef struct io_args_s
{
void *devPtr;
size_t max_size;
off_t offset;
off_t buf_off;
ssize_t read_bytes_done;
ssize_t write_bytes_done;
} io_args_t;
int main(int argc, char *argv[]) {
unsigned char iDigest[SHA256_DIGEST_LENGTH],
oDigest[SHA256_DIGEST_LENGTH];
<Get inputs>
<Create a data file using some random data>
// Allocate device Memory and register with cuFile
check_cudaruntimecall(cudaMalloc(&args.devPtr, args.max_size));
// Register buffers. For unregistered buffers, this call is not required.
status = cuFileBufRegister(args.devPtr, args.max_size, 0);
if (status.err != CU_FILE_SUCCESS) {
goto error;
}
< Open the data file just created for read and create a new data file to write the content
read from the datafile>
<Register the filehandles>
// Create stream for I/O.
check_cudaruntimecall(cudaStreamCreateWithFlags(&io_stream,
cudaStreamNonBlocking));
// Register Streams for best performance
// If all the inputs i.e. size, offset and buf_off are known and they are page aligned
// then use CU_FILE_STREAM_FIXED_AND_ALIGNED flag. If they are not known but
// will always be page aligned then use CU_FILE_STREAM_PAGE_ALIGNED_INPUTS
// flag.
check_cudaruntimecall(cuFileStreamRegister(io_stream,
CU_FILE_STREAM_FIXED_AND_ALIGNED));
// special case for holes
check_cudaruntimecall(cudaMemsetAsync(args.devPtr, 0, args.max_size, io_stream));
status = cuFileReadAsync(cf_rhandle, (unsigned char *)args.devPtr,
&args.max_size, &args.offset, &args.buf_off,
&args.read_bytes_done, io_stream);
if (status.err != CU_FILE_SUCCESS) {
std::cerr << "read failed : "
<< cuFileGetErrorString(status) << std::endl;
ret = -1;
goto error;
}
// Write loaded data from GPU memory to a new file
status = cuFileWriteAsync(cf_whandle, (unsigned char *)args.devPtr,
(size_t *)&args.max_size, &args.offset, &args.buf_off,
&args.write_bytes_done, io_stream);
if (status.err != CU_FILE_SUCCESS) {
goto error;
}
std::cout << "writing submit done to file :" << TEST_WRITEFILE << std::endl;
check_cudaruntimecall(cudaStreamSynchronize(io_stream));
if((args.read_bytes_done < (ssize_t)args.max_size) ||
(args.write_bytes_done < args.read_bytes_done))
{
std::cerr << "io error issued size:" << args.max_size <<
" read:" << args.read_bytes_done <<
" write:" << args.write_bytes_done << std::endl;
goto error;
}
// Compare file signatures
ret = SHASUM256(TEST_READWRITEFILE, iDigest, args.max_size);
if(ret < 0) {
…
}
DumpSHASUM(iDigest);
ret = SHASUM256(TEST_WRITEFILE, oDigest, args.max_size);
if(ret < 0) {
…
}
DumpSHASUM(oDigest);
if (memcmp(iDigest, oDigest, SHA256_DIGEST_LENGTH) != 0) {
std::cerr << "SHA SUM Mismatch" << std::endl;
ret = -1;
} else {
std::cout << "SHA SUM Match" << std::endl;
ret = 0;
}
if(io_stream) {
check_cudaruntimecall(cuFileStreamDeregister(io_stream));
check_cudaruntimecall(cudaStreamDestroy(io_stream));
}
<Free up all the resources>
return ret;
error:
…
}
This program demonstrates a simple use case where cuFile stream APIs can be used to perform a data integrity test using a single stream. It first creates a data file using random content. Then it reads the content through an I/O stream and writes that content into a new file. Finally it compares the content of the newly created data file against the original content using SHA (simple hash algorithm). It is possible that the exact size may not be known in the beginning and will be known later. In that scenario, one can set the actual size using the CUDA host call back function (cuLaunchHostFunc
) on the same stream before calling cuFileReadAsync
/cuFileWriteAsync
APIs.
3.4. cuFileHandleDeregister
Prerequisite: Before calling this API, the application must ensure that the IO on that handle has completed and is no longer being used. The file descriptor should be in an open state.
To reclaim resources before ending the process, always invoke the cuFileHandleDeregister
API.
3.5. cuFileBufDeregister
Prerequisite: Before calling this API, the application must ensure that all the cuFile IO operations that are using this buffer have completed.
For every buffer registered by using cuFileBufRegister
, use this API to deregister by using the same device pointer that was used for registration. This process ensures that all resources are reclaimed before ending the process.
3.6. cuFileStreamRegister
The cuFileStreamRegister
API converts a file descriptor to a cuFileHandle
and checks the ability of the named file, at its mount point, to be supported via GDS on this platform. Required.
Explicit stream registration with the cuFileStreamRegister
API is optional. If the stream is registered, then some internal buffers and associated metadata resources will be pre-allocated for subsequent stream I/O and would improve I/O latencies. Additionally these resources will be reused until deregistered using cuFileStreamUnregister
. Without this API, all these resources will be allocated during actual I/O.
cuFileStreamDeregister
Prerequisite: Before calling this API, the application must ensure that the I/O on that stream has completed and the stream is no longer being used
For every stream registered by using cuFileStreamRegister
, use this API to deregister by using the same stream that was used for registration. To reclaim resources before ending the process, always invoke this API.
3.8. cuFileDriverClose
Prerequisites: Before calling this API, the application must ensure that all the cuFile IO operations, buffers and handles are deregistered, and IO is completed.
In order to reduce the tear-down time of GDS enabled application (i.e. expedited release of GPU buffer pinnings and other cuFile resources), it is highly recommended to call the cuFileDriverClose()
API at the end of the application.
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