quickstart.rst

Quickstart

python

Basic usage

Calc squares of numbers:

import torch
from gpuparallel import GPUParallel, delayed

def perform(idx, gpu_id, **kwargs):
    tensor = torch.Tensor([idx]).to(gpu_id)
    return (tensor * tensor).item()

result = GPUParallel(n_gpu=2)(delayed(perform)(idx) for idx in range(5))
print(sorted(result))  # [0.0, 1.0, 4.0, 9.0, 16.0]

Initialize networks on worker init

Function init_fn is called on init of every worker. All common resources (e.g. networks) can be initialized here. In this example we create 32 workers on 16 GPUs, init model when workers are starting and then reuse workers for several batches of tasks:

from gpuparallel import GPUParallel, delayed

def init(gpu_id=None, **kwargs):
    global model
    model = load_model().to(gpu_id)

def perform(img, gpu_id=None, **kwargs):
    global model
    return model(img.to(gpu_id))

gp = GPUParallel(n_gpu=16, n_workers_per_gpu=2, init_fn=init)
results = gp(delayed(perform)(img) for img in fnames)

Reuse initialized workers

Once workers are initialized, they keep live until GPUParallel object exist. You can perform several queues of tasks without reinitializing worker resources:

gp = GPUParallel(n_gpu=16, n_workers_per_gpu=2, init_fn=init)
overall_results = []
for folder_images in folders:
    folder_results = gp(delayed(perform)(img) for img in folder_images)
    overall_results.extend(folder_results)
del gp  # this will close process pool to free memory

Simple logging from workers

Use log_to_stderr() call to init logging, and log.info(message) to log info from workers:

from gpuparallel import GPUParallel, delayed, log_to_stderr, log

log_to_stderr()

def perform(idx, worker_id=None, gpu_id=None):
    hi = f'Hello world #{idx} from worker #{worker_id} with GPU#{gpu_id}!'
    log.info(hi)

GPUParallel(n_gpu=2)(delayed(perform)(idx) for idx in range(2))

It will return:

[INFO/Worker-1(GPU1)]:Hello world #1 from worker #1 with GPU#1!
[INFO/Worker-0(GPU0)]:Hello world #0 from worker #0 with GPU#0!