I set up a new site (v3.0) currently and noticed it takes sometimes more than 20 seconds to save a page. On average it takes about 15 seconds but sometimes I have to wait up to 30 seconds before page is saved and the response message appears. I only added 2 text fields and 6 upload fields (for photos). Site is installed on my managed server with less than 20 other sites and none is a high-traffic site.
Unfortunately I don't have a special tool to test. But is there anything I can check why it is so slow?
The front-end loads quickly, only the admin area is slow and saving pages is even slower. I checked saving in Chrome without any add-ons installed. Nothing better.
Do you have the site running on your local machine to test to see if performance is an issue just on your server?
When you save a page, the onBefore/ onAfter write functions get called. It is possible you have code in those which may be executing slow (say you have something to email people when you publish a page). Or MySQL server could be slower in production than local. XHProf is a great tool to debug this information.
I have no copy on a local machine, but I've got other installations on the same server and all save pages much quicker. Each installation has got the same PHP version/settings and is tied to the same MySQL server. None of them is configured differently. However, I've tested different PHP versions (even FastCGI is slow). There is no customization for onBefore() or onAfter(). Actually there is nothing I can think of what makes this installation different.