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libgomp: Enable USM for some nvptx devices

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A few high-end nvptx devices support the attribute
CU_DEVICE_ATTRIBUTE_PAGEABLE_MEMORY_ACCESS; for those, unified shared
memory is supported in hardware. This patch enables support for those -
if all installed nvptx devices have this feature (as the capabilities
are per device type).

This exposes a bug in gomp_copy_back_icvs as it did before use
omp_get_mapped_ptr to find mapped variables, but that returns
the unchanged pointer in cased of shared memory. But in this case,
we have a few actually mapped pointers - like the ICV variables.
Additionally, there was a mismatch with regards to '-1' for the
device number as gomp_copy_back_icvs and omp_get_mapped_ptr count
differently. Hence, do the lookup manually.

include/ChangeLog:

	* cuda/cuda.h (CU_DEVICE_ATTRIBUTE_PAGEABLE_MEMORY_ACCESS): Add.

libgomp/ChangeLog:

	* libgomp.texi (nvptx): Update USM description.
	* plugin/plugin-nvptx.c (GOMP_OFFLOAD_get_num_devices):
	Claim support when requesting USM and all devices support
	CU_DEVICE_ATTRIBUTE_PAGEABLE_MEMORY_ACCESS.
	* target.c (gomp_copy_back_icvs): Fix device ptr lookup.
	(gomp_target_init): Set GOMP_OFFLOAD_CAP_SHARED_MEM is the
	devices supports USM.
This commit is contained in:
Tobias Burnus 2024-05-29 15:14:38 +02:00
parent 19c491d184
commit 4ccb3366ad
4 changed files with 45 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
include/cuda/cuda.h
View file

@ -83,7 +83,8 @@ typedef enum {
CU_DEVICE_ATTRIBUTE_MAX_THREADS_PER_MULTIPROCESSOR = 39,
CU_DEVICE_ATTRIBUTE_ASYNC_ENGINE_COUNT = 40,
CU_DEVICE_ATTRIBUTE_UNIFIED_ADDRESSING = 41,
CU_DEVICE_ATTRIBUTE_MAX_REGISTERS_PER_MULTIPROCESSOR = 82
CU_DEVICE_ATTRIBUTE_MAX_REGISTERS_PER_MULTIPROCESSOR = 82,
CU_DEVICE_ATTRIBUTE_PAGEABLE_MEMORY_ACCESS = 88
} CUdevice_attribute;
enum {

7
libgomp/libgomp.texi
View file

@ -6435,8 +6435,11 @@ The implementation remark:
the next reverse offload region is only executed after the previous
one returned.
@item OpenMP code that has a @code{requires} directive with
@code{unified_shared_memory} will remove any nvptx device from the
list of available devices (``host fallback'').
@code{unified_shared_memory} runs on nvptx devices if and only if
all of those support the @code{pageableMemoryAccess} property;@footnote{
@uref{https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#um-requirements}}
otherwise, all nvptx device are removed from the list of available
devices (``host fallback'').
@item The default per-warp stack size is 128 kiB; see also @code{-msoft-stack}
in the GCC manual.
@item The OpenMP routines @code{omp_target_memcpy_rect} and

15
libgomp/plugin/plugin-nvptx.c
View file

@ -1201,8 +1201,23 @@ GOMP_OFFLOAD_get_num_devices (unsigned int omp_requires_mask)
if (num_devices > 0
&& ((omp_requires_mask
& ~(GOMP_REQUIRES_UNIFIED_ADDRESS
| GOMP_REQUIRES_UNIFIED_SHARED_MEMORY
| GOMP_REQUIRES_REVERSE_OFFLOAD)) != 0))
return -1;
/* Check whether host page access (direct or via migration) is supported;
if so, enable USM. Currently, capabilities is per device type, hence,
check all devices. */
if (num_devices > 0
&& (omp_requires_mask & GOMP_REQUIRES_UNIFIED_SHARED_MEMORY))
for (int dev = 0; dev < num_devices; dev++)
{
int pi;
CUresult r;
r = CUDA_CALL_NOCHECK (cuDeviceGetAttribute, &pi,
CU_DEVICE_ATTRIBUTE_PAGEABLE_MEMORY_ACCESS, dev);
if (r != CUDA_SUCCESS || pi == 0)
return -1;
}
return num_devices;
}

24
libgomp/target.c
View file

@ -2969,8 +2969,25 @@ gomp_copy_back_icvs (struct gomp_device_descr *devicep, int device)
if (item == NULL)
return;
gomp_mutex_lock (&devicep->lock);
struct splay_tree_s *mem_map = &devicep->mem_map;
struct splay_tree_key_s cur_node;
void *dev_ptr = NULL;
void *host_ptr = &item->icvs;
void *dev_ptr = omp_get_mapped_ptr (host_ptr, device);
cur_node.host_start = (uintptr_t) host_ptr;
cur_node.host_end = cur_node.host_start;
splay_tree_key n = gomp_map_0len_lookup (mem_map, &cur_node);
if (n)
{
uintptr_t offset = cur_node.host_start - n->host_start;
dev_ptr = (void *) (n->tgt->tgt_start + n->tgt_offset + offset);
}
gomp_mutex_unlock (&devicep->lock);
if (dev_ptr != NULL)
gomp_copy_dev2host (devicep, NULL, host_ptr, dev_ptr,
sizeof (struct gomp_offload_icvs));
@ -5303,6 +5320,11 @@ gomp_target_init (void)
{
/* Augment DEVICES and NUM_DEVICES. */
/* If USM has been requested and is supported by all devices
of this type, set the capability accordingly. */
if (omp_requires_mask & GOMP_REQUIRES_UNIFIED_SHARED_MEMORY)
current_device.capabilities |= GOMP_OFFLOAD_CAP_SHARED_MEM;
devs = realloc (devs, (num_devs + new_num_devs)
* sizeof (struct gomp_device_descr));
if (!devs)