device/interface/device.cxx

#include "petscdevice_interface_internal.hpp" /*I <petscdevice.h> I*/
#include <petsc/private/petscadvancedmacros.h>

#include "../impls/host/hostdevice.hpp"
#include "../impls/cupm/cupmdevice.hpp"
#include "../impls/sycl/sycldevice.hpp"

#include <limits>  // std::numeric_limits
#include <utility> // std::make_pair

using namespace Petsc::device;

/*
  note to anyone adding more classes, the name must be ALL_CAPS_SHORT_NAME + Device exactly to
  be picked up by the switch-case macros below
*/
static host::Device HOSTDevice{PetscDeviceContextCreate_HOST};
#if PetscDefined(HAVE_CUDA)
static cupm::Device<cupm::DeviceType::CUDA> CUDADevice{PetscDeviceContextCreate_CUDA};
#endif
#if PetscDefined(HAVE_HIP)
static cupm::Device<cupm::DeviceType::HIP> HIPDevice{PetscDeviceContextCreate_HIP};
#endif
#if PetscDefined(HAVE_SYCL)
static sycl::Device SYCLDevice{PetscDeviceContextCreate_SYCL};
#endif

#define PETSC_DEVICE_CASE(IMPLS, func, ...) \
  case PetscConcat_(PETSC_DEVICE_, IMPLS): { \
    PetscCall(PetscConcat_(IMPLS, Device).func(__VA_ARGS__)); \
  } break

/*
  Suppose you have:

  CUDADevice.myFunction(arg1,arg2)

  that you would like to conditionally define and call in a switch-case:

  switch(PetscDeviceType) {
  #if PetscDefined(HAVE_CUDA)
  case PETSC_DEVICE_CUDA: {
    PetscCall(CUDADevice.myFunction(arg1,arg2));
  } break;
  #endif
  }

  then calling this macro:

  PETSC_DEVICE_CASE_IF_PETSC_DEFINED(CUDA,myFunction,arg1,arg2)

  will expand to the following case statement:

  case PETSC_DEVICE_CUDA: {
    PetscCall(CUDADevice.myFunction(arg1,arg2));
  } break

  if PetscDefined(HAVE_CUDA) evaluates to 1, and expand to nothing otherwise
*/
#define PETSC_DEVICE_CASE_IF_PETSC_DEFINED(IMPLS, func, ...) PetscIfPetscDefined(PetscConcat_(HAVE_, IMPLS), PETSC_DEVICE_CASE, PetscExpandToNothing)(IMPLS, func, __VA_ARGS__)

/*@C
  PetscDeviceCreate - Get a new handle for a particular device (often a GPU) type

  Not Collective

  Input Parameters:
+ type  - The type of `PetscDevice`
- devid - The numeric ID# of the device (pass `PETSC_DECIDE` to assign automatically)

  Output Parameter:
. device - The `PetscDevice`

  Notes:
  This routine may initialize `PetscDevice`. If this is the case, it may cause some sort of
  device synchronization.

  `devid` is what you might pass to `cudaSetDevice()` for example.

  Level: beginner

.seealso: `PetscDevice`, `PetscDeviceInitType`,
`PetscDeviceInitialize()`,`PetscDeviceInitialized()`, `PetscDeviceConfigure()`,
`PetscDeviceView()`, `PetscDeviceDestroy()`
@*/
PetscErrorCode PetscDeviceCreate(PetscDeviceType type, PetscInt devid, PetscDevice *device) {
  static PetscInt PetscDeviceCounter = 0;

  PetscFunctionBegin;
  PetscValidDeviceType(type, 1);
  PetscValidPointer(device, 3);
  PetscCall(PetscDeviceInitializePackage());
  PetscCall(PetscNew(device));
  (*device)->id     = PetscDeviceCounter++;
  (*device)->type   = type;
  (*device)->refcnt = 1;
  /*
    if you are adding a device, you also need to add it's initialization in
    PetscDeviceInitializeTypeFromOptions_Private() below
  */
  switch (type) {
    PETSC_DEVICE_CASE_IF_PETSC_DEFINED(HOST, getDevice, *device, devid);
    PETSC_DEVICE_CASE_IF_PETSC_DEFINED(CUDA, getDevice, *device, devid);
    PETSC_DEVICE_CASE_IF_PETSC_DEFINED(HIP, getDevice, *device, devid);
    PETSC_DEVICE_CASE_IF_PETSC_DEFINED(SYCL, getDevice, *device, devid);
  default:
    /* in case the above macros expand to nothing this silences any unused variable warnings */
    (void)(devid);
    SETERRQ(PETSC_COMM_SELF, PETSC_ERR_PLIB, "PETSc was seemingly configured for PetscDeviceType %s but we've fallen through all cases in a switch", PetscDeviceTypes[type]);
  }
  PetscFunctionReturn(0);
}

/*@C
  PetscDeviceDestroy - Free a `PetscDevice`

  Not Collective

  Input Parameter:
. device - The `PetscDevice`

  Level: beginner

.seealso: `PetscDevice`, `PetscDeviceCreate()`, `PetscDeviceConfigure()`, `PetscDeviceView()`,
`PetscDeviceGetType()`, `PetscDeviceGetDeviceId()`
@*/
PetscErrorCode PetscDeviceDestroy(PetscDevice *device) {
  PetscFunctionBegin;
  PetscValidPointer(device, 1);
  if (!*device) PetscFunctionReturn(0);
  PetscValidDevice(*device, 1);
  PetscCall(PetscDeviceDereference_Internal(*device));
  if ((*device)->refcnt) {
    *device = nullptr;
    PetscFunctionReturn(0);
  }
  PetscCall(PetscFree((*device)->data));
  PetscCall(PetscFree(*device));
  PetscFunctionReturn(0);
}

/*@C
  PetscDeviceConfigure - Configure a particular `PetscDevice`

  Not Collective

  Input Parameter:
. device - The `PetscDevice` to configure

  Notes:
  The user should not assume that this is a cheap operation.

  Level: beginner

.seealso: `PetscDevice`, `PetscDeviceCreate()`, `PetscDeviceView()`, `PetscDeviceDestroy()`,
`PetscDeviceGetType()`, `PetscDeviceGetDeviceId()`
@*/
PetscErrorCode PetscDeviceConfigure(PetscDevice device) {
  PetscFunctionBegin;
  PetscValidDevice(device, 1);
  /*
    if no available configuration is available, this cascades all the way down to default
    and error
  */
  switch (const auto dtype = device->type) {
  case PETSC_DEVICE_HOST:
    if (PetscDefined(HAVE_HOST)) break; // always true
  case PETSC_DEVICE_CUDA:
    if (PetscDefined(HAVE_CUDA)) break;
    goto error;
  case PETSC_DEVICE_HIP:
    if (PetscDefined(HAVE_HIP)) break;
    goto error;
  case PETSC_DEVICE_SYCL:
    if (PetscDefined(HAVE_SYCL)) break;
    goto error;
  default:
  error:
    SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "PETSc was not configured for PetscDeviceType %s", PetscDeviceTypes[dtype]);
  }
  PetscUseTypeMethod(device, configure);
  PetscFunctionReturn(0);
}

/*@C
  PetscDeviceView - View a `PetscDevice`

  Collective on viewer

  Input Parameters:
+ device - The `PetscDevice` to view
- viewer - The `PetscViewer` to view the device with (`NULL` for `PETSC_VIEWER_STDOUT_WORLD`)

  Level: beginner

.seealso: `PetscDevice`, `PetscDeviceCreate()`, `PetscDeviceConfigure()`,
`PetscDeviceDestroy()`, `PetscDeviceGetType()`, `PetscDeviceGetDeviceId()`
@*/
PetscErrorCode PetscDeviceView(PetscDevice device, PetscViewer viewer) {
  auto      sub = viewer;
  PetscBool iascii;

  PetscFunctionBegin;
  PetscValidDevice(device, 1);
  if (viewer) {
    PetscValidHeaderSpecific(viewer, PETSC_VIEWER_CLASSID, 2);
    PetscCall(PetscObjectTypeCompare(PetscObjectCast(viewer), PETSCVIEWERASCII, &iascii));
  } else {
    PetscCall(PetscViewerASCIIGetStdout(PETSC_COMM_WORLD, &viewer));
    iascii = PETSC_TRUE;
  }

  if (iascii) {
    auto        dtype = PETSC_DEVICE_HOST;
    MPI_Comm    comm;
    PetscMPIInt size;
    PetscInt    id = 0;

    PetscCall(PetscObjectGetComm(PetscObjectCast(viewer), &comm));
    PetscCallMPI(MPI_Comm_size(comm, &size));

    PetscCall(PetscDeviceGetDeviceId(device, &id));
    PetscCall(PetscDeviceGetType(device, &dtype));
    PetscCall(PetscViewerGetSubViewer(viewer, PETSC_COMM_SELF, &sub));
    PetscCall(PetscViewerASCIIPrintf(sub, "PetscDevice Object: %d MPI %s\n", size, size == 1 ? "process" : "processes"));
    PetscCall(PetscViewerASCIIPushTab(sub));
    PetscCall(PetscViewerASCIIPrintf(sub, "type: %s\n", PetscDeviceTypes[dtype]));
    PetscCall(PetscViewerASCIIPrintf(sub, "id: %" PetscInt_FMT "\n", id));
  }

  // see if impls has extra viewer stuff
  PetscTryTypeMethod(device, view, sub);

  if (iascii) {
    // undo the ASCII specific stuff
    PetscCall(PetscViewerASCIIPopTab(sub));
    PetscCall(PetscViewerRestoreSubViewer(viewer, PETSC_COMM_SELF, &sub));
    PetscCall(PetscViewerFlush(viewer));
  }
  PetscFunctionReturn(0);
}

/*@C
  PetscDeviceGetType - Get the type of device

  Not Collective

  Input Parameter:
. device - The `PetscDevice`

  Output Parameter:
. type - The `PetscDeviceType`

  Level: beginner

.seealso: `PetscDevice`, `PetscDeviceType`, `PetscDeviceSetDefaultDeviceType()`,
`PetscDeviceCreate()`, `PetscDeviceConfigure()`, `PetscDeviceDestroy()`,
`PetscDeviceGetDeviceId()`, `PETSC_DEVICE_DEFAULT()`
@*/
PetscErrorCode PetscDeviceGetType(PetscDevice device, PetscDeviceType *type) {
  PetscFunctionBegin;
  PetscValidDevice(device, 1);
  PetscValidPointer(type, 2);
  *type = device->type;
  PetscFunctionReturn(0);
}

/*@C
  PetscDeviceGetDeviceId - Get the device ID for a `PetscDevice`

  Not Collective

  Input Parameter:
. device - The `PetscDevice`

  Output Parameter:
. id - The id

  Notes:
  The returned ID may have been assigned by the underlying device backend. For example if the
  backend is CUDA then `id` is exactly the value returned by `cudaGetDevice()` at the time when
  this device was configured.

  Level: beginner

.seealso: `PetscDevice`, `PetscDeviceCreate()`, `PetscDeviceGetType()`
@*/
PetscErrorCode PetscDeviceGetDeviceId(PetscDevice device, PetscInt *id) {
  PetscFunctionBegin;
  PetscValidDevice(device, 1);
  PetscValidIntPointer(id, 2);
  *id = device->deviceId;
  PetscFunctionReturn(0);
}

struct DefaultDeviceType : public Petsc::RegisterFinalizeable<DefaultDeviceType> {
  PetscDeviceType type = PETSC_DEVICE_HARDWARE_DEFAULT_TYPE;

  PETSC_NODISCARD PetscErrorCode finalize_() noexcept {
    PetscFunctionBegin;
    type = PETSC_DEVICE_HARDWARE_DEFAULT_TYPE;
    PetscFunctionReturn(0);
  }
};

static auto default_device_type = DefaultDeviceType();

/*@C
  PETSC_DEVICE_DEFAULT - Retrieve the current default `PetscDeviceType`

  Not Collective

  Notes:
  Unless selected by the user, the default device is selected in the following order\:
  `PETSC_DEVICE_HIP`, `PETSC_DEVICE_CUDA`, `PETSC_DEVICE_SYCL`, `PETSC_DEVICE_HOST`.

  Level: beginner

.seealso: `PetscDeviceType`, `PetscDeviceSetDefaultDeviceType()`, `PetscDeviceGetType()`
@*/
PetscDeviceType PETSC_DEVICE_DEFAULT(void) {
  return default_device_type.type;
}

/*@C
  PetscDeviceSetDefaultDeviceType - Set the default device type for `PetscDevice`

  Not Collective

  Input Parameter:
. type - the new default device type

  Notes:
  This sets the `PetscDeviceType` returned by `PETSC_DEVICE_DEFAULT()`.

  Level: beginner

.seealso: `PetscDeviceType`, `PetscDeviceGetType`,
@*/
PetscErrorCode PetscDeviceSetDefaultDeviceType(PetscDeviceType type) {
  PetscFunctionBegin;
  PetscValidDeviceType(type, 1);
  if (default_device_type.type != type) {
    // no need to waster a PetscRegisterFinalize() slot if we don't change it
    default_device_type.type = type;
    PetscCall(default_device_type.register_finalize());
  }
  PetscFunctionReturn(0);
}

static std::array<std::pair<PetscDevice, bool>, PETSC_DEVICE_MAX> defaultDevices = {};

/*
  Actual intialization function; any functions claiming to initialize PetscDevice or
  PetscDeviceContext will have to run through this one
*/
static PetscErrorCode PetscDeviceInitializeDefaultDevice_Internal(PetscDeviceType type, PetscInt defaultDeviceId) {
  PetscFunctionBegin;
  PetscValidDeviceType(type, 1);
  if (PetscUnlikely(!PetscDeviceInitialized(type))) {
    auto &dev  = defaultDevices[type].first;
    auto &init = defaultDevices[type].second;

    PetscAssert(!dev, PETSC_COMM_SELF, PETSC_ERR_MEM, "Trying to overwrite existing default device of type %s", PetscDeviceTypes[type]);
    PetscCall(PetscDeviceCreate(type, defaultDeviceId, &dev));
    PetscCall(PetscDeviceConfigure(dev));
    init = true;
  }
  PetscFunctionReturn(0);
}

/*@C
  PetscDeviceInitialize - Initialize `PetscDevice`

  Not Collective

  Input Parameter:
. type - The `PetscDeviceType` to initialize

  Notes:
  Eagerly initializes the corresponding `PetscDeviceType` if needed. If this is the case it may
  result in device synchronization.

  Level: beginner

.seealso: `PetscDevice`, `PetscDeviceInitType`, `PetscDeviceInitialized()`,
`PetscDeviceCreate()`, `PetscDeviceDestroy()`
@*/
PetscErrorCode PetscDeviceInitialize(PetscDeviceType type) {
  PetscFunctionBegin;
  PetscValidDeviceType(type, 1);
  PetscCall(PetscDeviceInitializeDefaultDevice_Internal(type, PETSC_DECIDE));
  PetscFunctionReturn(0);
}

/*@C
  PetscDeviceInitialized - Determines whether `PetscDevice` is initialized for a particular
  `PetscDeviceType`

  Not Collective

  Input Parameter:
. type - The `PetscDeviceType` to check

  Notes:
  Returns `PETSC_TRUE` if `type` is initialized, `PETSC_FALSE` otherwise.

  If one has not configured PETSc for a particular `PetscDeviceType` then this routine will
  return `PETSC_FALSE` for that `PetscDeviceType`.

  Level: beginner

.seealso: `PetscDevice`, `PetscDeviceInitType`, `PetscDeviceInitialize()`,
`PetscDeviceCreate()`, `PetscDeviceDestroy()`
@*/
PetscBool PetscDeviceInitialized(PetscDeviceType type) {
  return static_cast<PetscBool>(PetscDeviceConfiguredFor_Internal(type) && defaultDevices[type].second);
}

/* Get the default PetscDevice for a particular type and constructs them if lazily initialized. */
PetscErrorCode PetscDeviceGetDefaultForType_Internal(PetscDeviceType type, PetscDevice *device) {
  PetscFunctionBegin;
  PetscValidPointer(device, 2);
  PetscCall(PetscDeviceInitialize(type));
  *device = defaultDevices[type].first;
  PetscFunctionReturn(0);
}

/*@C
  PetscDeviceGetAttribute - Query a particular attribute of a `PetscDevice`

  Not Collective

  Input Parameters:
+ device - The `PetscDevice`
- attr   - The attribute

  Output Parameter:
. value - The value of the attribute

  Notes:
  Since different attributes are often different types `value` is a `void *` to accommodate
  them all. The underlying type of the attribute is therefore included in the name of the
  `PetscDeviceAttribute` reponsible for querying it. For example,
  `PETSC_DEVICE_ATTR_SIZE_T_SHARED_MEM_PER_BLOCK` is of type `size_t`.

  Level: intermediate

.seealso: `PetscDeviceAtrtibute`, `PetscDeviceConfigure()`, `PetscDevice`
@*/
PetscErrorCode PetscDeviceGetAttribute(PetscDevice device, PetscDeviceAttribute attr, void *value) {
  PetscFunctionBegin;
  PetscValidDevice(device, 1);
  PetscValidDeviceAttribute(attr, 2);
  PetscValidPointer(value, 3);
  PetscUseTypeMethod(device, getattribute, attr, value);
  PetscFunctionReturn(0);
}

static PetscErrorCode PetscDeviceInitializeTypeFromOptions_Private(MPI_Comm comm, PetscDeviceType type, PetscInt defaultDeviceId, PetscBool defaultView, PetscDeviceInitType *defaultInitType) {
  PetscFunctionBegin;
  if (!PetscDeviceConfiguredFor_Internal(type)) {
    PetscCall(PetscInfo(nullptr, "PetscDeviceType %s not available\n", PetscDeviceTypes[type]));
    defaultDevices[type].first = nullptr;
    PetscFunctionReturn(0);
  }
  PetscCall(PetscInfo(nullptr, "PetscDeviceType %s available, initializing\n", PetscDeviceTypes[type]));
  /* ugly switch needed to pick the right global variable... could maybe do this as a union? */
  switch (type) {
    PETSC_DEVICE_CASE_IF_PETSC_DEFINED(HOST, initialize, comm, &defaultDeviceId, &defaultView, defaultInitType);
    PETSC_DEVICE_CASE_IF_PETSC_DEFINED(CUDA, initialize, comm, &defaultDeviceId, &defaultView, defaultInitType);
    PETSC_DEVICE_CASE_IF_PETSC_DEFINED(HIP, initialize, comm, &defaultDeviceId, &defaultView, defaultInitType);
    PETSC_DEVICE_CASE_IF_PETSC_DEFINED(SYCL, initialize, comm, &defaultDeviceId, &defaultView, defaultInitType);
  default: SETERRQ(comm, PETSC_ERR_PLIB, "PETSc was seemingly configured for PetscDeviceType %s but we've fallen through all cases in a switch", PetscDeviceTypes[type]);
  }
  PetscCall(PetscInfo(nullptr, "PetscDevice %s initialized, default device id %" PetscInt_FMT ", view %s, init type %s\n", PetscDeviceTypes[type], defaultDeviceId, PetscBools[defaultView], PetscDeviceInitTypes[Petsc::util::integral_value(*defaultInitType)]));
  /*
    defaultInitType, defaultView  and defaultDeviceId now represent what the individual TYPES
    have decided to initialize as
  */
  if ((*defaultInitType == PETSC_DEVICE_INIT_EAGER) || defaultView) {
    PetscCall(PetscInfo(nullptr, "Eagerly initializing %s PetscDevice\n", PetscDeviceTypes[type]));
    PetscCall(PetscDeviceInitializeDefaultDevice_Internal(type, defaultDeviceId));
    if (defaultView) PetscCall(PetscDeviceView(defaultDevices[type].first, nullptr));
  }
  PetscFunctionReturn(0);
}

static PetscErrorCode PetscDeviceInitializeQueryOptions_Private(MPI_Comm comm, PetscDeviceType *deviceContextInitDevice, PetscDeviceInitType *defaultInitType, PetscInt *defaultDevice, PetscBool *defaultDeviceSet, PetscBool *defaultView) {
  PetscInt initIdx       = PETSC_DEVICE_INIT_LAZY;
  auto     initDeviceIdx = static_cast<PetscInt>(*deviceContextInitDevice);
  auto     flg           = PETSC_FALSE;

  PetscFunctionBegin;
  PetscCall(PetscOptionsHasName(nullptr, nullptr, "-log_view_gpu_time", &flg));
  if (flg) PetscCall(PetscLogGpuTime());

  PetscOptionsBegin(comm, nullptr, "PetscDevice Options", "Sys");
  PetscCall(PetscOptionsEList("-device_enable", "How (or whether) to initialize PetscDevices", "PetscDeviceInitialize()", PetscDeviceInitTypes, 3, PetscDeviceInitTypes[initIdx], &initIdx, nullptr));
  PetscCall(PetscOptionsEList("-default_device_type", "Set the PetscDeviceType returned by PETSC_DEVICE_DEFAULT()", "PetscDeviceSetDefaultDeviceType()", PetscDeviceTypes, PETSC_DEVICE_MAX, PetscDeviceTypes[initDeviceIdx], &initDeviceIdx, defaultDeviceSet));
  PetscCall(PetscOptionsRangeInt("-device_select", "Which device to use. Pass " PetscStringize(PETSC_DECIDE) " to have PETSc decide or (given they exist) [0-" PetscStringize(PETSC_DEVICE_MAX_DEVICES) ") for a specific device", "PetscDeviceCreate()", *defaultDevice, defaultDevice, nullptr, PETSC_DECIDE, PETSC_DEVICE_MAX_DEVICES));
  PetscCall(PetscOptionsBool("-device_view", "Display device information and assignments (forces eager initialization)", "PetscDeviceView()", *defaultView, defaultView, &flg));
  PetscOptionsEnd();

  if (initIdx == PETSC_DEVICE_INIT_NONE) {
    /* disabled all device initialization if devices are globally disabled */
    PetscCheck(*defaultDevice == PETSC_DECIDE, comm, PETSC_ERR_USER_INPUT, "You have disabled devices but also specified a particular device to use, these options are mutually exlusive");
    *defaultView  = PETSC_FALSE;
    initDeviceIdx = PETSC_DEVICE_HOST;
  } else {
    *defaultView = static_cast<PetscBool>(*defaultView && flg);
    if (*defaultView) initIdx = PETSC_DEVICE_INIT_EAGER;
  }
  *defaultInitType         = PetscDeviceInitTypeCast(initIdx);
  *deviceContextInitDevice = PetscDeviceTypeCast(initDeviceIdx);
  PetscFunctionReturn(0);
}

/* called from PetscFinalize() do not call yourself! */
static PetscErrorCode PetscDeviceFinalize_Private() {
  PetscFunctionBegin;
  if (PetscDefined(USE_DEBUG)) {
    const auto PetscDeviceCheckAllDestroyedAfterFinalize = [] {
      PetscFunctionBegin;
      for (auto &&device : defaultDevices) {
        const auto dev = device.first;

        PetscCheck(!dev, PETSC_COMM_WORLD, PETSC_ERR_COR, "Device of type '%s' had reference count %" PetscInt_FMT " and was not fully destroyed during PetscFinalize()", PetscDeviceTypes[dev->type], dev->refcnt);
      }
      PetscFunctionReturn(0);
    };
    /*
      you might be thinking, why on earth are you registered yet another finalizer in a
      function already called during PetscRegisterFinalizeAll()? If this seems stupid it's
      because it is.

      The crux of the problem is that the initializer (and therefore the ~finalizer~) of
      PetscDeviceContext is guaranteed to run after PetscDevice's. So if the global context had
      a default PetscDevice attached, that PetscDevice will have a reference count >0 and hence
      won't be destroyed yet. So we need to repeat the check that all devices have been
      destroyed again ~after~ the global context is destroyed. In summary:

      1. This finalizer runs and destroys all devices, except it may not because the global
         context may still hold a reference!
      2. The global context finalizer runs and does the final reference count decrement
         required, which actually destroys the held device.
      3. Our newly added finalizer runs and checks that all is well.
    */
    PetscCall(PetscRegisterFinalize(std::move(PetscDeviceCheckAllDestroyedAfterFinalize)));
  }
  for (auto &&device : defaultDevices) {
    PetscCall(PetscDeviceDestroy(&device.first));
    device.second = false;
  }
  PetscFunctionReturn(0);
}

/*
  Begins the init proceeedings for the entire PetscDevice stack. there are 3 stages of
  initialization types:

  1. defaultInitType - how does PetscDevice as a whole expect to initialize?
  2. subTypeDefaultInitType - how does each PetscDevice implementation expect to initialize?
     e.g. you may want to blanket disable PetscDevice init (and disable say Kokkos init), but
     have all CUDA devices still initialize.

  All told the following happens:

  0. defaultInitType -> LAZY
  1. Check for log_view/log_summary, if yes defaultInitType -> EAGER
  2. PetscDevice initializes each sub type with deviceDefaultInitType.
  2.1 Each enabled PetscDevice sub-type then does the above disable or view check in addition
      to checking for specific device init. if view or specific device init
      subTypeDefaultInitType -> EAGER. disabled once again overrides all.
*/

PetscErrorCode PetscDeviceInitializeFromOptions_Internal(MPI_Comm comm) {
  auto defaultView                    = PETSC_FALSE;
  auto initializeDeviceContextEagerly = PETSC_FALSE;
  auto defaultDeviceSet               = PETSC_FALSE;
  auto defaultDevice                  = PetscInt{PETSC_DECIDE};
  auto deviceContextInitDevice        = PETSC_DEVICE_DEFAULT();
  auto defaultInitType                = PETSC_DEVICE_INIT_LAZY;

  PetscFunctionBegin;
  if (PetscDefined(USE_DEBUG)) {
    int result;

    PetscCallMPI(MPI_Comm_compare(comm, PETSC_COMM_WORLD, &result));
    /* in order to accurately assign ranks to gpus we need to get the MPI_Comm_rank of the
     * global space */
    if (PetscUnlikely(result != MPI_IDENT)) {
      char name[MPI_MAX_OBJECT_NAME] = {};
      int  len; /* unused */

      PetscCallMPI(MPI_Comm_get_name(comm, name, &len));
      SETERRQ(comm, PETSC_ERR_MPI, "Default devices being initialized on MPI_Comm '%s' not PETSC_COMM_WORLD", name);
    }
  }
  comm = PETSC_COMM_WORLD; /* from this point on we assume we're on PETSC_COMM_WORLD */
  PetscCall(PetscRegisterFinalize(PetscDeviceFinalize_Private));

  PetscCall(PetscDeviceInitializeQueryOptions_Private(comm, &deviceContextInitDevice, &defaultInitType, &defaultDevice, &defaultDeviceSet, &defaultView));

  // the precise values don't matter here, so long as they are sequential
  static_assert(Petsc::util::integral_value(PETSC_DEVICE_HOST) == 0, "");
  static_assert(Petsc::util::integral_value(PETSC_DEVICE_CUDA) == 1, "");
  static_assert(Petsc::util::integral_value(PETSC_DEVICE_HIP) == 2, "");
  static_assert(Petsc::util::integral_value(PETSC_DEVICE_SYCL) == 3, "");
  static_assert(Petsc::util::integral_value(PETSC_DEVICE_MAX) == 4, "");
  for (int i = PETSC_DEVICE_HOST; i < PETSC_DEVICE_MAX; ++i) {
    const auto deviceType = PetscDeviceTypeCast(i);
    auto       initType   = defaultInitType;

    PetscCall(PetscDeviceInitializeTypeFromOptions_Private(comm, deviceType, defaultDevice, defaultView, &initType));
    if (PetscDeviceConfiguredFor_Internal(deviceType)) {
      if (initType == PETSC_DEVICE_INIT_EAGER) {
        initializeDeviceContextEagerly = PETSC_TRUE;
        // only update the default device if the user hasn't set it previously
        if (!defaultDeviceSet) {
          deviceContextInitDevice = deviceType;
          PetscCall(PetscInfo(nullptr, "PetscDevice %s set as default device type due to eager initialization\n", PetscDeviceTypes[deviceType]));
        }
      } else if (initType == PETSC_DEVICE_INIT_NONE) {
        if (deviceType != PETSC_DEVICE_HOST) PetscCheck(deviceType != deviceContextInitDevice, comm, PETSC_ERR_USER_INPUT, "Cannot explicitly disable the device set as default device type (%s)", PetscDeviceTypes[deviceType]);
      }
    }
  }

  PetscCall(PetscDeviceSetDefaultDeviceType(deviceContextInitDevice));
  PetscCall(PetscDeviceContextSetRootDeviceType_Internal(PETSC_DEVICE_DEFAULT()));
  /* ----------------------------------------------------------------------------------- */
  /*                       PetscDevice is now fully initialized                          */
  /* ----------------------------------------------------------------------------------- */
  {
    /*
      query the options db to get the root settings from the user (if any).

      This section is a bit of a hack. We have to reach across to dcontext.cxx to all but call
      PetscDeviceContextSetFromOptions() before we even have one, then set a few static
      variables in that file with the results.
    */
    auto dtype = std::make_pair(PETSC_DEVICE_DEFAULT(), PETSC_FALSE);
    auto stype = std::make_pair(PETSC_DEVICE_CONTEXT_DEFAULT_STREAM_TYPE, PETSC_FALSE);

    PetscOptionsBegin(comm, "root_", "Root PetscDeviceContext Options", "Sys");
    PetscCall(PetscDeviceContextQueryOptions_Internal(PetscOptionsObject, dtype, stype));
    PetscOptionsEnd();

    if (dtype.second) PetscCall(PetscDeviceContextSetRootDeviceType_Internal(dtype.first));
    if (stype.second) PetscCall(PetscDeviceContextSetRootStreamType_Internal(stype.first));
  }

  if (initializeDeviceContextEagerly) {
    PetscDeviceContext dctx;

    PetscCall(PetscInfo(nullptr, "Eagerly initializing PetscDeviceContext with %s device\n", PetscDeviceTypes[deviceContextInitDevice]));
    /* instantiates the device context */
    PetscCall(PetscDeviceContextGetCurrentContext(&dctx));
    PetscCall(PetscDeviceContextSetUp(dctx));
  }
  PetscFunctionReturn(0);
}