Los Angeles County knife laws are the same as Los Angeles Municipal knife laws, only the statute/code numbers are different. It is a violation of both LA County and LA Municipal laws to openly carry any knife with a blade 3 or more inches long in public. However there are exception to these laws, like if you are carrying the knife for "legitimate" purpose like work, camping, fishing, etc, and can prove it.
Here is a link to the official Los Angeles County website-
http://www.lacounty.gov
And here is a link that can be found using that website that provides all of La County laws-
https://www.municode.com/library/ca/los_angeles_county/code_of_ordinances (type "knife" into the search box at the top of the screen to find the LA county knife laws).
And here are code numbers from the LA county codes- 13.62.010 (how they define a "knife"- a blade 3" or longer)
13.62.020 (what is illegal to do with a "knife" with a blade 3" or longer)
As far as being arrested or stopped/hassled by the cops, there can be several determining factors, like your demeanor/appearance, your location, what you are doing, the attitude of any individual cop who sees the knife, etc, etc.