Runtime Settings

Compatibility Mode KVIKIO_COMPAT_MODE

When KvikIO is running in compatibility mode, it doesn’t load libcufile.so. Instead, reads and writes are done using POSIX. Notice, this is not the same as the compatibility mode in cuFile. It is possible that KvikIO performs I/O in the non-compatibility mode by using the cuFile library, but the cuFile library itself is configured to operate in its own compatibility mode. For more details, refer to cuFile compatibility mode and cuFile environment variables .

The environment variable KVIKIO_COMPAT_MODE has three options (case-insensitive):

  • ON (aliases: TRUE, YES, 1): Enable the compatibility mode.

  • OFF (aliases: FALSE, NO, 0): Disable the compatibility mode, and enforce cuFile I/O. GDS will be activated if the system requirements for cuFile are met and cuFile is properly configured. However, if the system is not suited for cuFile, I/O operations under the OFF option may error out, crash or hang.

  • AUTO: Try cuFile I/O first, and fall back to POSIX I/O if the system requirements for cuFile are not met.

Under AUTO, KvikIO falls back to the compatibility mode:

  • when libcufile.so cannot be found.

  • when running in Windows Subsystem for Linux (WSL).

  • when /run/udev isn’t readable, which typically happens when running inside a docker image not launched with --volume /run/udev:/run/udev:ro.

This setting can also be programmatically controlled by kvikio.defaults.set_compat_mode() and kvikio.defaults.compat_mode_reset().

Thread Pool KVIKIO_NTHREADS

KvikIO can use multiple threads for IO automatically. Set the environment variable KVIKIO_NTHREADS to the number of threads in the thread pool. If not set, the default value is 1.

This setting can also be controlled by kvikio.defaults.get_num_threads(), kvikio.defaults.num_threads_reset(), and kvikio.defaults.set_num_threads().

Task Size KVIKIO_TASK_SIZE

KvikIO splits parallel IO operations into multiple tasks. Set the environment variable KVIKIO_TASK_SIZE to the maximum task size (in bytes). If not set, the default value is 4194304 (4 MiB).

This setting can also be controlled by kvikio.defaults.task_size(), kvikio.defaults.task_size_reset(), and kvikio.defaults.set_task_size().

GDS Threshold KVIKIO_GDS_THRESHOLD

In order to improve performance of small IO, .pread() and .pwrite() implement a shortcut that circumvent the threadpool and use the POSIX backend directly. Set the environment variable KVIKIO_GDS_THRESHOLD to the minimum size (in bytes) to use GDS. If not set, the default value is 1048576 (1 MiB).

This setting can also be controlled by kvikio.defaults.gds_threshold(), kvikio.defaults.gds_threshold_reset(), and kvikio.defaults.set_gds_threshold().

Size of the Bounce Buffer KVIKIO_BOUNCE_BUFFER_SIZE

KvikIO might have to use intermediate host buffers (one per thread) when copying between files and device memory. Set the environment variable KVIKIO_BOUNCE_BUFFER_SIZE to the size (in bytes) of these “bounce” buffers. If not set, the default value is 16777216 (16 MiB).

This setting can also be controlled by kvikio.defaults.bounce_buffer_size(), kvikio.defaults.bounce_buffer_size_reset(), and kvikio.defaults.set_bounce_buffer_size().