Rendering small amounts of markdown is VERY slow, e.g. 0.2+ seconds for
about 4 lines of markdown with very little formatting.
Is this a known issue? How do you work around it? Do you format before
save or during render?
Yes, it's extremely slow. One of the better options you have is to
have a separate column in the database for storing the formatted
version, which you save when the unformatted version is changed. There
was a plugin like "filtered_column" for this, but it's a really easy
hook to add in anyway.
Alternatively, you can use fragment caching to cache the portions of
pages you run through markdown.