ncclResult_t region_get_coll_info_internal_v3()

in src/tuner/nccl_ofi_regions.cpp [982:1047]

• 52 lines of code
• 11 McCabe index (conditional complexity)

ncclResult_t region_get_coll_info_internal_v3(nccl_ofi_tuner_context_t *ctx,
					   ncclFunc_t collType,
					   size_t nBytes,
					   int numPipeOps,
					   float **collCostTable,
					   int numAlgo,
					   int numProto,
					   int *nChannels)
{
	ncclResult_t ret = ncclSuccess;
	nccl_ofi_tuner_region_context_t *region_ctx = (nccl_ofi_tuner_region_context_t *)ctx->type_ctx;
	float(*table)[NCCL_NUM_PROTOCOLS] = (float(*)[NCCL_NUM_PROTOCOLS])collCostTable;
	int in_out = -1;
	int algorithm = NCCL_ALGO_UNDEF;
	int protocol = NCCL_PROTO_UNDEF;
	nccl_ofi_tuner_point_t p;

	if (region_ctx == NULL || region_ctx->regions[collType] == NULL) {
		/* we do not update cost table. Fall back to NCCL's tuner */
		NCCL_OFI_INFO(NCCL_TUNING, "Region Context is not ready. Fall back to NCCL's tuner.");
		ret = ncclSuccess;
		goto exit;
	}

	/* Skip when two nodes or lesser because the regions are not well defined and fallback
	 * to NCCL's internal tunings */
	if (region_ctx->dims.num_nodes <= 2) {
		ret = ncclSuccess;
		goto exit;
	}
	
	p.x = (double)nBytes;
	p.y = (double)region_ctx->dims.num_ranks;

	/* Check all regions */
	for (size_t i = 0; i < region_ctx->num_regions[collType] && in_out < 0; i++) {
		algorithm = region_ctx->regions[collType][i].algorithm;
		protocol = region_ctx->regions[collType][i].protocol;
		if (algorithm >= numAlgo || protocol >= numProto ||
		    table[algorithm][protocol] == NCCL_ALGO_PROTO_IGNORE) {
			/* Either NCCL says this combination is not valid/applicable or the algorithm or protocol is
			 * not in the table, hence it is not supported by this NCCL version. */
			continue;
		}

		in_out = is_inside_region(p, &region_ctx->regions[collType][i]);
		if (in_out >= 0) {
			table[algorithm][protocol] = 0.0;

			NCCL_OFI_INFO(NCCL_TUNING,
				      "Region Tuner choosing algo %d proto %d with cost %.8f µsecs for coll %d size %ld.",
				      algorithm,
				      protocol,
				      table[algorithm][protocol],
				      collType,
				      nBytes);
		}
	}

	if (in_out < 0) {
		NCCL_OFI_INFO(NCCL_TUNING, "Falling back to NCCL's tuner for coll %d size %ld.", collType, nBytes);
	}

exit:
	return ret;
}