What is an XPerf alternative for Linux and Mac OS X?

For OS X, look into dtrace and derived tools (I think fs_usage and sc_usage are related; there's also a Linux port), as well as parts of Apple's Developer Tools such as Shark (see e.g. here and here).

For linux you can combine many tools. top (or htop), iotop, etc. You could also install BSD accounting and use the sa command.