A method for managing I/O event notifications in a data processing system, the data processing system comprising a plurality of applications and an operating system having a kernel and an I/O event notification mechanism operable to maintain a plurality of I/O event notification objects each handling a set of file descriptors associated with one or more I/O resources, the method comprising: for each of a plurality of application-level configuration calls: intercepting at a user-level interface a configuration call from an application to the I/O event notification mechanism for configuring an I/O event notification object; and storing a set of parameters of the configuration call at a data structure, each set of parameters representing an operation on the set of file descriptors handled by the I/O event notification object; and subsequently, on a predetermined criterion being met: the user-level interface causing the plurality of configuration calls to be effected by means of a first system call to the kernel.