CLENQUEUEMIGRATEMEMO(3clc)

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✨ CLENQUEUEMIGRATEMEMO ✨

okay bestie, gather round 💖 you're reading a page from the OpenCL Manual, section 3clc, and it's all about clEnqueueMigrateMemObjects — the girlboss function that tells OpenCL which device your memory objects should be living on. no cap, this one's a banger.

🌸 NAME 🌸

clEnqueueMigrateMemObjects — enqueues a command to indicate which device a set of memory objects should be associated with. literally that's it. that's the job. 💅

🦋 SYNOPSIS 🦋

cl_int clEnqueueMigrateMemObjects(cl_command_queue command_queue,
                                  cl_uint num_mem_objects,
                                  const cl_mem *mem_objects,
                                  cl_mem_migration_flags flags,
                                  cl_uint num_events_in_wait_list,
                                  const cl_event *event_wait_list,
                                  cl_event *event);

look at her. seven arguments. main character energy fr fr 👑

🎀 PARAMETERS 🎀

  • command_queue — a valid command-queue. the memory objects you pass in mem_objects get migrated to the OpenCL device that's chillin' with this command_queue, OR to the host if you specified CL_MIGRATE_MEM_OBJECT_HOST. pick your fighter 💫
  • num_mem_objects — the number of memory objects you're passing in mem_objects. count them, bestie, don't guess 🔢
  • mem_objects — a pointer to a list of memory objects. the whole squad 🫶
  • flags — a bit-field that specifies your migration options. here's the tea on what values it can take:
    • CL_MIGRATE_MEM_OBJECT_HOST — this flag says the specified set of memory objects are to be migrated to the host, regardless of the target command-queue. host said "come here" and the command-queue doesn't get a vote 🏠
    • CL_MIGRATE_MEM_OBJECT_CONTENT_UNDEFINED — this flag says the contents of the set of memory objects are undefined after migration. the specified set of memory objects are migrated to the device associated with command_queue without incurring the overhead of migrating their contents. it's giving "move the box but don't bother packing it" 📦💀
  • event_wait_list, num_events_in_wait_list — these specify events that need to complete before this particular command can even be executed. if event_wait_list is NULL, then this particular command does not wait on any event to complete. if event_wait_list is NULL, num_events_in_wait_list must be 0. if event_wait_list is not NULL, the list of events pointed to by event_wait_list must be valid and num_events_in_wait_list must be greater than 0. the events specified in event_wait_list act as synchronization points. the context associated with events in event_wait_list and command_queue must be the same. the memory associated with event_wait_list can be reused or freed after the function returns. so like, free it whenever, she's not holding onto it 🔓
  • event — returns an event object that identifies this particular command and can be used to query or queue a wait for this particular command to complete. event can be NULL, in which case it will not be possible for the application to query the status of this command or queue a wait for this command to complete. if the event_wait_list and the event arguments are not NULL, the event argument should not refer to an element of the event_wait_list array. don't make her point at herself, that's weird 🙈

💜 NOTES 💜

this section describes a mechanism for assigning which device an OpenCL memory object resides. a user may wish to have more explicit control over the location of their memory objects on creation. this could be used to:

  • Ensure that an object is allocated on a specific device prior to usage.
  • Preemptively migrate an object from one device to another.

Typically, memory objects are implicitly migrated to a device for which enqueued commands, using the memory object, are targeted. clEnqueueMigrateMemObjects allows this migration to be explicitly performed ahead of the dependent commands. This allows a user to preemptively change the association of a memory object, through regular command queue scheduling, in order to prepare for another upcoming command. This also permits an application to overlap the placement of memory objects with other unrelated operations before these memory objects are needed potentially hiding transfer latencies. Once the event, returned from clEnqueueMigrateMemObjects, has been marked CL_COMPLETE the memory objects specified in mem_objects have been successfully migrated to the device associated with command_queue. The migrated memory object shall remain resident on the device until another command is enqueued that either implicitly or explicitly migrates it away.

clEnqueueMigrateMemObjects can also be used to direct the initial placement of a memory object, after creation, possibly avoiding the initial overhead of instantiating the object on the first enqueued command to use it.

The user is responsible for managing the event dependencies, associated with this command, in order to avoid overlapping access to memory objects. Improperly specified event dependencies passed to clEnqueueMigrateMemObjects could result in undefined results.

🚨 bestie listen: you are responsible for managing the event dependencies. improperly specified event dependencies could result in undefined results. that's the scary kind of undefined. be careful, okay? 🫂

🔥 ERRORS 🔥

clEnqueueMigrateMemObjects returns CL_SUCCESS if the function is executed successfully. otherwise, it returns one of the following errors:

  • CL_INVALID_COMMAND_QUEUE if command_queue is not a valid command_queue.
  • CL_INVALID_CONTEXT if the context associated with command_queue and memory objects in memobj are not the same or if the context associated with command_queue and events in event_wait_list are not the same.
  • CL_INVALID_MEM_OBJECT if any of the memory objects in mem_objs is not a valid memory object.
  • CL_INVALID_VALUE if num_mem_objects is zero or if mem_objects is NULL.
  • CL_INVALID_VALUE if flags is not 0 or is not any of the values described in the table above.
  • CL_INVALID_EVENT_WAIT_LIST if event_wait_list is NULL and num_events_in_wait_list > 0, or event_wait_list is not NULL and num_events_in_wait_list is 0, or if event objects in event_wait_list are not valid events.
  • CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to allocate memory for the specified set of memory objects in mem_objects.
  • CL_OUT_OF_RESOURCES if there is a failure to allocate resources required by the OpenCL implementation on the device.
  • CL_OUT_OF_HOST_MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.

⭐ SPECIFICATION ⭐

OpenCL Specification[1]

🌈 SEE ALSO 🌈

clEnqueueMapBuffer(3clc), clEnqueueMapImage(3clc)

go read those next, they're also iconic iykyk 📚✨

👑 AUTHORS 👑

The Khronos Group

Copyright © 2007-2011 The Khronos Group Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and/or associated documentation files (the "Materials"), to deal in the Materials without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Materials, and to permit persons to whom the Materials are furnished to do so, subject to the condition that this copyright notice and permission notice shall be included in all copies or substantial portions of the Materials.

🧚 NOTES (the footnote one) 🧚

  1. OpenCL Specification — page 123, section 5.4.4 - Migrating Memory Objects

and that's a wrap on the whole page, bestie 🎀 this edition of the OpenCL Manual was brought to you by The Khronos Group, dated 01/14/2021, filed under CLENQUEUEMIGRATEMEMO(3clc). go migrate something responsibly. mwah 💋

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