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# SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: Apache-2.0
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import math
import os
import pynvml
class Device:
"""A class to handle NVIDIA GPU device operations using NVML.
This class provides an interface to access and manage NVIDIA GPU devices,
including retrieving device information and CPU affinity settings.
Attributes:
_nvml_affinity_elements (int): Number of 64-bit elements needed to represent CPU affinity
"""
_nvml_affinity_elements = math.ceil(os.cpu_count() / 64) # type: ignore
def __init__(self, device_idx: int):
"""Initialize a Device instance for a specific GPU.
Args:
device_idx (int): Index of the GPU device to manage
Raises:
NVMLError: If the device cannot be found or initialized
"""
super().__init__()
self.handle = pynvml.nvmlDeviceGetHandleByIndex(device_idx)
def get_cpu_affinity(self) -> list[int]:
"""Get the CPU affinity mask for this GPU device.
Retrieves the CPU affinity mask indicating which CPU cores are assigned
to this GPU device. The affinity is returned as a list of CPU core indices.
Returns:
list[int]: List of CPU core indices that have affinity with this GPU
Raises:
NVMLError: If the CPU affinity information cannot be retrieved
Example:
>>> device = Device(0)
>>> device.get_cpu_affinity()
[0, 1, 2, 3] # Shows this GPU has affinity with CPU cores 0-3
"""
affinity_string = ""
for j in pynvml.nvmlDeviceGetCpuAffinity(self.handle, Device._nvml_affinity_elements):
# assume nvml returns list of 64 bit ints
affinity_string = "{:064b}".format(j) + affinity_string
affinity_list = [int(x) for x in affinity_string]
affinity_list.reverse() # so core 0 is in 0th element of list
return [i for i, e in enumerate(affinity_list) if e != 0]
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