Epoll optimisations
A method for managing I/O event notifications in a 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. 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, upon meeting a predetermined criterion: the user-level interface causing the plurality of configuration calls to be effected by means of a first system call to the kernel.
1. A method for processing a blocking system call at a data processing system comprising an operating system that supports kernel and user-level contexts, the method comprising:
intercepting a blocking system call from an entity running in a kernel context or user-level context, wherein when executed the blocking system call invokes an operation and blocks until the operation occurs;
in response to intercepting the blocking system call, instead of executing the blocking system call, repeatedly executing the system call in non-blocking mode for a first timeout period; and
in response to determining that the system call in non-blocking mode has not returned a value within the first timeout period, subtracting the first timeout period from a second timeout period and executing the blocking system call for a remainder of the second timeout period after subtraction.
2. A method as claimed in claim 1 , further comprising, in response to determining that the system call in non-blocking mode has not returned a value within the first timeout period, enabling interrupts for the entity.
3. A method as claimed in claim 1 , wherein the system call is executed in non-blocking mode with a third timeout of zero.
4. A method as claimed in claim 1 , wherein the intercepting step is performed in the kernel context.
5. A method as claimed in claim 1 , wherein the intercepting step is performed at a user-level interface, the user-level interface:
replacing the blocking system call with a new system call; and
causing, by means of the new system call, the step of repeatedly executing the system call in non-blocking mode to be performed in the kernel context.
6. A method as claimed in claim 1 , wherein the data processing system comprises a plurality of CPU cores.
7. A method as claimed in claim 1 , wherein the step of repeatedly executing the system call in non-blocking mode further comprises not enabling interrupts for the entity whilst the system call is being repeatedly executed in non-blocking mode.
8. A method as claimed in claim 1 , wherein the step of repeatedly executing the system call in non-blocking mode further comprises not enabling interrupts for the entity in respect of the system calls.
9. A method as claimed in claim 1 , wherein the operating system is Linux and the blocking system call is one of epoll( ) select( ) poll( ) read( ) write( ), send( ) recv( ) accept( ) and futex( ).
10. A method as claimed in claim 1 , wherein the first timeout period expresses a maximum number of times that the system call is to be executed in non-blocking mode.
11. A data processing system comprising a memory and one or more processors coupled to the memory, the one or more processors configured to execute an operating system that supports kernel and user-level contexts, the memory having stored therein a plurality of software code portions defining logic for:
intercepting a blocking system call from an entity running in a kernel context or user-level context, wherein when executed the blocking system call invokes an operation and blocks until the operation occurs;
in response to intercepting the blocking system call, instead of executing the blocking system call repeatedly executing the system call in non-blocking mode for a first timeout period; and
in response to determining that the system call in non-blocking mode has not returned a value within the first timeout period, subtracting the first timeout period from a second timeout period and executing the blocking system call for a remainder of the second timeout period after subtraction.