# Multi-site fixel-based analysis: 2-step population template creation? **URL:** \ **Category:** Uncategorized\ **Created:** [May 15, 2017, 7:42pm UTC](https://community.mrtrix.org/t/multi-site-fixel-based-analysis-2-step-population-template-creation/893 "2017-05-15T19:42:02Z")\ **Posts on this page:** 1\ **Showing post:** 9
**Author:** ![maxpietsch](https://community.mrtrix.org/user_avatar/community.mrtrix.org/maxpietsch/32/25_2.png) [@maxpietsch](https://community.mrtrix.org/u/maxpietsch)\ **Post date:** [May 23, 2017, 10:11am UTC](https://community.mrtrix.org/t/multi-site-fixel-based-analysis-2-step-population-template-creation/893/9 "2017-05-23T10:11:20Z")
Without more information I can only add some random guesses: `dwiintensitynorm` uses `population_template` which as of [this commit](https://github.com/MRtrix3/mrtrix3/commit/58e51affd027e1c193996e) has double the number of linear registration stages. I have never run it on such a huge population but it should not increase the computation time by two orders of magnitude. The [dirty pages](http://community.mrtrix.org/t/linux-fs-recommendations/891) [issue](http://community.mrtrix.org/t/trouble-with-mrtrix3-and-mrtrix2/790/5) could cause such a decrease in performance but I can not think of any recent changes to the code that might have increased this problem. Can you monitor the CPU and machine load with `top`. If there is a swapping issue then the `load average` is high but the `CPU wa` is low. > [@rgrazioplene](#): > > Oh–one key difference that might be important is that I’m using symbolic links to the dwi and mask data this time. Not sure if that could have anything to do with it but just in case… What is the old version you are referring to? We changed the behaviour of `dwiintensitynorm` regarding symbolic links in November. `population_template`’s temporary directory is created inside `dwiintensitynorm`’s. So if this used to be in RAM and now is on disk, this might impact performance. Also, if it is now in RAM and you run out of RAM then swapping will cause this decrease in performance. --- _[View the full topic](https://community.mrtrix.org/t/multi-site-fixel-based-analysis-2-step-population-template-creation/893)._