How to choose pct_start in OneCycleScheduler?

[yang-zhang]

This post explains what pct_start means very well. But I have trouble finding how to choose pct_start. What impact does pct_start have on model training? Why was it set to a different value from the default 0.3 in these notebooks:

• https://github.com/fastai/course-v3/blob/master/nbs/dl1/lesson3-camvid.ipynb
• https://github.com/fastai/course-v3/blob/master/nbs/dl1/lesson7-human-numbers.ipynb

Thanks.

[sgugger]

Through trial and error
More seriously, sometimes initial training requires a really long warm_up (hence the 0.9 in the first notebook) and on contrary, fine-tuning often barely requires a warmup at all (hence the 0.1 in the second).

[yang-zhang]

This makes a lot of sense. Thanks!