On Thu, Mar 27, 2014 at 7:14 PM, Ulrich Pegelow <ulrich.pege...@tongareva.de > wrote:
> Am 26.03.2014 22:33, schrieb Christian Kanzian: > > Am Mittwoch, 26. März 2014 schrieb jerome: > > > >> So is this normal ? > >> I mean, core use and the fact I need export only one at time ? > >> > >> Sorry for long story but it help to understand how and why. > >> > >> And sorry for my bad english ;) > >> > >> Thanks to all > > > > Within OpenCL the GPU does the parallel thing for you. > > > > There is a blog post on that [0]. According to that you have to set > "export > > multiple images in parallel" to 1. BTW this setting was removed sometime > ago > > from the GUI or I can't find it anymore. > > That's mostly correct. If you set that option (parallel_export) to > something higher than 1 darktable starts that many export threads in > parallel. Any available OpenCL device gets allocated to one of the > parallel threads, all remaining threads are processed on CPU. > and maybe just to add to this: even the cpu code path will use multiple cores to process your images, it will just not export multiple images in parallel (but parallelize the work within one image). j. > > If you have two GPUs with the same speed, it makes a lot of sense to set > parallel_export to 2. However, in most cases users have only one GPU > that is often much faster than the CPU. Or few people have two GPUs with > a big performance difference. In these cases you only profit from > multiple parallel export threads, if you export *many* images in one > step. In case of few images to export you always need to wait until the > slowest device is finished and it often be faster to process all of them > on the fastest device only. > > @Jerome: what was said before, only should affect the speed. In your > case it seems that export hangs at some point. You should start > darktable with option '-d opencl' to see what happens. If you share that > debug output here we might be able to help. > > Does your system completely freeze? The power supply of your computer > needs to be strong enough to feed two GPUs in parallel. If not, voltage > will drop and you may get a hardware crash. > > Ulrich > > > > > ------------------------------------------------------------------------------ > _______________________________________________ > darktable-devel mailing list > darktable-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/darktable-devel >
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