The NVML does not return the correct strut for latest CUDA.

[fostiropoulos]

For my current system

| NVIDIA-SMI 535.54.03              Driver Version: 535.54.03    CUDA Version: 12.2     |

The processes running on cuda are read incorrectly. There is an additional size_t element when reading the strut that is not documented but when ignored causes the response to be malformed.

The following code illustrates the error:

from collections import namedtuple
from ctypes import *
import time

import pynvml
import ray
from pynvml.nvml import (
    _nvmlGetFunctionPointer,
    _PrintableStructure,
    nvmlDeviceGetComputeRunningProcesses,
)
import torch
import struct

Process = namedtuple(
    "Process", ["pid", "usedGpuMemory", "gpuInstanceId", "computeInstanceId"]
)

def _remote_fn():
    torch.randn(100).to("cuda")
    time.sleep(10)

def run_bug():
    pynvml.nvmlInit()
    handle = pynvml.nvmlDeviceGetHandleByIndex(0)
    # this initializes and creates an additional process (for added difficulty)
    a = torch.randn(100).to("cuda")
    for i in range(10):
        (
            ray.remote(
                num_gpus=0.001,
                num_cpus=0.001,
                max_calls=1,
                max_retries=0,
            )(_remote_fn)
            .options(name="x")
            .remote()
        )
    # wait for all processes to be allocated
    time.sleep(4)
    procs = nvmlDeviceGetComputeRunningProcesses(handle)

    class c_nvmlProcessInfo_t(_PrintableStructure):
        _fields_ = [
            ("pid", c_uint),
            ("usedGpuMemory", c_ulonglong),
            ("gpuInstanceId", c_uint),
            ("computeInstanceId", c_uint),
            ("index", c_ssize_t),
        ]
        _fmt_ = {
            "usedGpuMemory": "%d B",
        }

    pynvml.nvml.c_nvmlProcessInfo_t = c_nvmlProcessInfo_t

    procs_fixed = nvmlDeviceGetComputeRunningProcesses(handle)

    def _parse_result(procs):
        return "\n".join(str(p) for p in procs)

    return _parse_result(procs), _parse_result(procs_fixed)

def get_procs_analysis():
    pynvml.nvmlInit()
    handle = pynvml.nvmlDeviceGetHandleByIndex(0)
    fn = _nvmlGetFunctionPointer("nvmlDeviceGetComputeRunningProcesses_v3")
    # Reference
    # https://docs.nvidia.com/deploy/nvml-api/structnvmlProcessInfo__t.html#structnvmlProcessInfo__t
    # although the order differs (e.g. pid, usedGpuMemory, gpuInstanceId, computeInstanceId)
    # NOTE, I am not sure which is which for the last 2 as they are identical on my system
    # and not possible to debug.
    expr = "IQIIn"
    byte_size_proc = struct.calcsize(expr)
    # ORIGINAL
    proc_array = c_ubyte * (byte_size_proc * 100)  # enough for 100 processes
    c_procs = proc_array()

    # make the call again
    c_count = c_uint(100)

    ret = fn(handle, byref(c_count), c_procs)
    return_bytes = bytes(c_procs)

    def _parse_bytes(idx):
        args = struct.unpack(
            expr,
            return_bytes[idx * byte_size_proc : (idx + 1) * byte_size_proc],
        )
        return Process(*args[:-1])

    formatted = []
    for i in range(100):
        p = _parse_bytes(i)
        if p.pid == 0 and p.usedGpuMemory == 0 and p.gpuInstanceId == 0:
            break
        formatted.append(str(p))

    return '\n'.join(formatted)

if __name__ == "__main__":
    procs, procs_fixed = run_bug()
    print(procs)
    print(procs_fixed)
    print(get_procs_analysis())

Output:

{'pid': 1183425, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295}
{'pid': 0, 'usedGpuMemory': 1280123, 'gpuInstanceId': 251658240, 'computeInstanceId': 0}
{'pid': 4294967295, 'usedGpuMemory': 0, 'gpuInstanceId': 1283310, 'computeInstanceId': 0}
{'pid': 251658240, 'usedGpuMemory': None, 'gpuInstanceId': 0, 'computeInstanceId': 0}
{'pid': 1283307, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295}
{'pid': 0, 'usedGpuMemory': 1283309, 'gpuInstanceId': 251658240, 'computeInstanceId': 0}
{'pid': 4294967295, 'usedGpuMemory': 0, 'gpuInstanceId': 1283311, 'computeInstanceId': 0}
{'pid': 251658240, 'usedGpuMemory': None, 'gpuInstanceId': 0, 'computeInstanceId': 0}
{'pid': 1283308, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295}
{'pid': 0, 'usedGpuMemory': 1283306, 'gpuInstanceId': 251658240, 'computeInstanceId': 0}
{'pid': 4294967295, 'usedGpuMemory': 0, 'gpuInstanceId': 1283313, 'computeInstanceId': 0}
{'pid': 251658240, 'usedGpuMemory': None, 'gpuInstanceId': 0, 'computeInstanceId': 0}

Expected:

{'pid': 1183425, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1280123, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283310, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283307, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283309, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283311, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283308, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283306, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283313, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283312, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283315, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}
{'pid': 1283314, 'usedGpuMemory': 251658240, 'gpuInstanceId': 4294967295, 'computeInstanceId': 4294967295, 'index': 0}

[fostiropoulos]

Having tried the same code in different machine with different GPUs the error seems to be related to the GPU model. The code that produces a bug is from RTX 2080 with nvlink, while the same code does not produce an error for V100.

[wence-]

Thanks. This is due to an inadvertent ABI break in the 535 driver, which will fixed in the next patch release.

[fostiropoulos]

Thanks for clarifying. Should there be a check somewhere and an error raised for this particular version or documentation of it?

[erikhuck]

@wence- Patch release for what? nvidia? cuda? Or can the pynvml package be updated to fix this?

[erikhuck]

this may be the same problem as my issue here: #50

[fostiropoulos]

@erikhuck how I solved it was to uninstall driver version 535 and install the preceding release until the newer version is released.

| NVIDIA-SMI 525.125.06   Driver Version: 525.125.06   CUDA Version: 12.0     |