OpenMP "feature" causes massive performance issues on multi-cores

[Andreas Sandberg]

Binary package hint: ufraw

The parallelization of UFRaw is so bad that it is actually (a lot) faster to run it with OMP_NUM_THREADS=1 to disable OpenMP parallelizations on my Core2 Quad. It seems like the parallelization was done over too small chunks to amortize the thread startup cost.

I'd suggest disabling OpenMP support in UFRaw to improve performance. The current version is barely usable, the slowdown is probably (at least) 10x.

ProblemType: Bug
Architecture: amd64
Date: Sun Oct 11 01:10:46 2009
DistroRelease: Ubuntu 9.10
NonfreeKernelModules: fglrx
Package: ufraw 0.15-2ubuntu1
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-13.43-generic
SourcePackage: ufraw
Uname: Linux 2.6.31-13-generic x86_64

[Oli (oli)]

Using an i7 here and yes, it's deathly slow.

Strange thing is, a few weeks ago this was flying along at a nice speed. Was the OpenMP patch that recent?

[Vladimir (snape)]

Yes. I have same experience. On my Intel Core 2Quad Q8300 (2,5GHz 4MB) it takes over one minute to change EV Exposure Compensation. As soon, as I start ufraw with OMP_NUM_THREADS=1, the change is almost instant (less than 2 seconds).

[gavomatic57 (gavomatic57)]

I'm having the same issues - UFRaw 1.5 and Ubuntu 9.10 x64, Core i7 920, 6gb RAM.
Kernel 2.6.31-16-generic

Out of interest, how do you run it with OMP_NUM_THREADS=1?

[Vladimir (snape)]

2 gavomatic57:

Just type

   # OMP_NUM_THREADS=1 ufraw

or you can add it permanently by adding a line to a .bashrc file

    export OMP_NUM_THREADS=1

[Andrew Dodd (atd7)]

THANK YOU! UFraw has been effectively unusable for me since switching this machine from Gentoo to Ubuntu 9.10 - OMP_NUM_THREADS=1 fixed the problem.

[Andrew Dodd (atd7)]

I should have put more information in my post:
Ubuntu 9.10, Core 2 Quad Q6600.

When loading a PEF image from a Pentax camera, the preview window takes forever to draw, and performance is very variable and unpredictable. UFRaw will just freeze periodically after drawing a few tiles. This also affects anything that causes the preview window to change, such as exposure changes.

When OMP_NUM_THREADS is set to 1 as an environment variable, preview redraws are fast and predictable in the time they take.