フィルターのクリア

Why is my parfor loop running slower than a regular for loop

6 ビュー (過去 30 日間)
tiwwexx
tiwwexx 2023 年 12 月 19 日
回答済み: Christine Tobler 2023 年 12 月 19 日
Hello all, I have a 3D array that takes an SVD of the first two dimensions for the size of the 3rd dimension. This seems like it would be extreemly parallelizable to me so I tried to run it in a parfor loop but for some reason the computation is like 10x slower running the parfor vs the standard for loop. Any help will be much appriciated!!
im_vec = rand(4,4,1000);
U = zeros(size(im_vec,1),size(im_vec,1),size(im_vec,3));
sig = zeros(size(im_vec));
V = zeros(size(im_vec,2),size(im_vec,2),size(im_vec,3));
%%% For loop time %%%
tic
for n = 1:size(im_vec,3)
[U(:,:,n), sig(:,:,n),V(:,:,n)] = svd(im_vec(:,:,n));
end
toc
%%% Parfor loop time %%%
p = gcp('nocreate');
if isempty(p)
parpool;
end
tic
parfor n = 1:size(im_vec,3)
[U(:,:,n), sig(:,:,n),V(:,:,n)] = svd(im_vec(:,:,n));
end
toc
  1 件のコメント
Walter Roberson
Walter Roberson 2023 年 12 月 19 日
On my system, if I expand the work by a factor of 100, then the regular for loop takes about 0.58 seconds and the parfor loop takes about 0.22 seconds the first time (and about 0.15 seconds after that.)

サインインしてコメントする。

回答 (1 件)

Christine Tobler
Christine Tobler 2023 年 12 月 19 日
The problem is likely that the cost of each iteration is still too small to warrant the start-up time of the parfor loop.
You could take a look at the pagesvd function, which applies the SVD to each page A(:, :, i) of the input array, just like what you're doing here. It uses threading on a lower level when the size of the array means we expect the threading to be worthwhile.

カテゴリ

Help Center および File ExchangeLoops and Conditional Statements についてさらに検索

製品


リリース

R2023b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by