Special:Version on labs requires digging out the info from git for each extension, this comes down to git show on each extension, which takes far too long. Either information should be cached and we should be clever about how we check that the cached info for an ext is no longer valid, or we should get the info for multiple repos in a batch, instead of shelling out separately for each one.
Representative is this output: Served by deployment-apache33 in 28.877 secs. See http://en.wikipedia.beta.wmflabs.org/wiki/Special:Version to test for yourselves.
T49265: Option to disable showing dates of git commits in Special:Version