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DALI Environment Variables#

This page lists environment variables used by DALI. Note that those variables often control internal behavior of DALI and are subject to change without notice.

Memory management#

DALI_USE_DEVICE_MEM_POOL#

Values: 0, 1

Default: 1

If nonzero, DALI uses a memory pool for device memory; otherwise plain cudaMalloc is used.

Warning

Specify 0 for debugging only, doing so will drastically degrade performance.

DALI_USE_VMM#

Values: 0, 1

Default: 1

If nonzero, DALI uses a memory pool based on virtual memory management functions (cuMemCreate, cuMemMap, etc) when possible. If disabled, DALI will use a pool based on cudaMalloc.

DALI_USE_PINNED_MEM_POOL#

Values: 0, 1

Default: 1

If nonzero, DALI uses a memory pool for device-accessible host memory; otherwise plain cudaMallocHost is used.

Warning

Specify 0 for debugging only, doing so will drastically degrade performance.

DALI_USE_CUDA_MALLOC_ASYNC#

Values: 0, 1

Default: 0

If enabled, DALI will use cudaMallocAsync as the device memory allocation mechanism. This flag is not compatible with DALI_USE_DEVICE_MEM_POOL=0 and explicitly enabling DALI_USE_VMM=1.

DALI_MALLOC_POOL_THRESHOLD#

Values: >= 0, optionally followed by k for KiB or M for MiB.

Default: 0

If nonzero, dali uses an internal memory pool for regular host memory below the specified size.

DALI_GDS_CHUNK_SIZE#

Values: powers of 2, 4k to 16M, with optional k or M suffix

Default: 2M

The size of memory chunk used by GPU Direct Storage in DALI.

DALI_HOST_BUFFER_SHRINK_THRESHOLD#

Values: floating point, 0..1

Default: 0.5

If set, buffers resized to below the given fraction of capacity will be shrunk to fit the data.

DALI_BUFFER_GROWTH_FACTOR#

Values: floating point, >=1

Default: 1.1

When greater than 1, buffers are allocated with allowance to avoid frequent reallocation.

DALI_HOST_BUFFER_GROWTH_FACTOR#

Specialized version of DALI_BUFFER_GROWTH_FACTOR for CPU buffers only.

DALI_DEVICE_BUFFER_GROWTH_FACTOR#

Specialized version of DALI_BUFFER_GROWTH_FACTOR for GPU buffers only.

DALI_RESTRICT_PINNED_MEM#

Values: 0, 1

Default: 0

If enabled, DALI will reduce the use of pinned host memory; useful on systems where the amount of pinned memory is restricted (e.g. WSL).

Image decoding#

DALI_MAX_JPEG_SCANS#

Values: >= 1

Default: 256

The maximum number of progressive JPEG scans. Specify lower values to mitigate maliciously malformed JPEGs, designed for denial of service attacks.

DALI_NVIMGCODEC_LOG_LEVEL#

Values: 1..5

Default: 2

The verbosity of logs produced by nvJPEG

Miscellaneous#

DALI_OPTIMIZE_GRAPH#

Values: 0, 1

Default: 1

For debugging only; if set to 0, all DALI graph optimizations are disabled.

DALI_ENABLE_CSE#

Values: 0, 1

Default: 1

For debugging only; if set to 0, the common subexpression elimination (CSE) graph optimization is disabled. If DALI_OPTIMIZE_GRAPH is disabled, this flag has no effect.

DALI_USE_EXEC2#

Values: 0, 1

Default: 0

If set, DALI will use the default execution model (as if exec_dynamic=True was set in the Pipeline) whenever the default asynchronous pipelined execution with uniform queue size is specified. Enabling this flag can potentially improve memory consumption.

Note

This flag is used in the backend only; the Python frontend is unaware of it and doesn’t enable the new features and optimizations that would be enabled by specifying exec_dynamic=True in the pipeline.

DALI_AFFINITY_MASK#

Values: comma-separated list of CPU IDs

Default: empty

Sets the thread affinity. The number of entries in the list must match the num_threads passed to the pipeline. Requires NVML.

DALI_PRELOAD_PLUGINS#

Values: colon-separated list of paths

Default: empty

If specified, DALI will preload plugins specified in this list.

DALI_DISABLE_NVML#

Values: 0, 1

Default: 0

If set, DALI doesn’t try to use NVML. Useful on systems without NVML support, e.g. WSL2.

Network#

AWS_ENDPOINT_URL#

Values: a URL, e.g. http://127.0.0.1:9000

Default: unset (the AWS SDK resolves the regional S3 endpoint)

Overrides the endpoint used for s3:// paths, which allows DALI to read from an S3-compatible service such as MinIO. The value must include the scheme; without it the AWS SDK assumes https://.

Note

DALI uses the AWS SDK default addressing mode. When the endpoint host is a host name, requests are addressed as <scheme>://<bucket>.<host>, which requires a matching DNS entry to exist. When the host is an IP literal, path-style addressing (<scheme>://<host>/<bucket>) is used instead.

Note

The value is read once, when the S3 client is created on the first s3:// access in the process. Changing it afterwards has no effect.

Credentials and region are taken from the standard AWS variables (AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_DEFAULT_REGION).

DALI_S3_NO_VERIFY_SSL#

Values: 0, 1

Default: 0

If set, DALI will not verify SSL certificates when communicating with S3 services.

By default, DALI uses SSL when communicating with S3 services, which includes verifying SSL certificates. This option allows you to override the default behavior of verifying SSL certificates.

DALI_GCS_ENDPOINT_URL#

Values: a URL, e.g. http://127.0.0.1:4443

Default: unset (the client talks to Google Cloud Storage)

Overrides the endpoint used for gs:// paths, which allows DALI to read from a Google Cloud Storage emulator. The value must include the scheme.

Note

The value is read once, when the GCS client is created on the first gs:// access in the process. Changing it afterwards has no effect.

DALI_GCS_ANONYMOUS#

Values: 0, 1

Default: 0

If set, DALI accesses gs:// paths without credentials. By default the client uses Application Default Credentials, which neither a public bucket nor a local emulator requires - reading either one means opting out of authentication explicitly.

Note

The value is read once, when the GCS client is created on the first gs:// access in the process. Changing it afterwards has no effect.

DALI_GCS_VERIFY_CHECKSUMS#

Values: 0, 1

Default: 0

If set, DALI validates the CRC32C checksum of the data it downloads from gs:// paths.

DALI only ever issues ranged reads, while Google Cloud Storage reports checksums for whole objects only, so a per-read checksum cannot be validated end to end - which is why this is off by default and costs CPU in the data loading path when turned on. It is meant for debugging.

Note

The value is read once, when the GCS client is created on the first gs:// access in the process. Changing it afterwards has no effect.

DALI_GCS_REQUEST_TIMEOUT_SEC#

Values: a non-negative integer number of seconds

Default: 60

Bounds how long a single gs:// request may take. A transfer that receives no bytes for this long is aborted, and the retry loop around it gives up once this much time has elapsed, so an unreachable endpoint surfaces an error after roughly twice this value in the worst case.

Transient errors from Google Cloud Storage are still retried with exponential backoff; the default leaves room for about six attempts. Set the value to 0 to restore the google-cloud-cpp defaults instead - a 120 second stall timeout and a 15 minute retry window - which lets the pipeline hang for up to a quarter of an hour with no output against a dead or misrouted endpoint.

Note

The value is read once, when the GCS client is created on the first gs:// access in the process. Changing it afterwards has no effect.

Testing#

DALI_EXTRA_PATH#

Values: path

Default: empty

The path to where the contents of DALI_extra repository reside. Necessary to run DALI tests.