Second-order tuning of spin loops
A method and/or computer for a tuned spin count in a multithreaded system determines a re-calculation time interval at which to re-calculate a current spin lock value. Then, a spin-lock-re-calculation is repeatedly executed at the re-calculation time interval to perform: observing a current environment of the multithreaded system, determining, using a second-order tuning and values of the current environment, a dynamically calculated heuristic to provide the newly-recalculated spin lock value, and memorizing the newly re-calculated spin lock value, in a memory, as the current spin lock value. Meanwhile, thread(s) in the multithreaded system which want to execute a spinlock will obtain the current spin lock value which is memorized in the memory, and execute the spin lock using the current spin lock value to set a length of the spin lock.
1. A method for a tuned spin count in a multithreaded system, comprising:
determining, in a processor, a re-calculation time interval at which to re-calculate a current spin lock value;
repeatedly executing, by the processor, at the re-calculation time interval, a spin-lock-re-calculation that performs steps of:
observing a current environment of the multithreaded system,
determining, using a second-order tuning and values of the current environment, a dynamically calculated heuristic to provide the newly-recalculated spin lock value, and
memorizing the newly re-calculated spin lock value, in a memory cooperatively operable with the processor, as the current spin lock value; and
obtaining, by the processor, in at least one thread, the current spin lock value which is memorized in the memory, and executing a spin lock in the at least one thread using the current spin lock value to set a length of the spin lock.
2. The method of claim 1 , wherein the re-calculation time interval at which the spin-lock-re-calculation is executed to observe the current environment is calculated as a constant ratio of a signal call time.
3. The method of claim 1 , wherein the re-calculation time interval is determined using a first-order tuning which uses an exponentially weighted moving average (EWMA) of time taken to signal another thread.
4. The method of claim 1 , wherein the current environment which is observed by the spin-lock-re-calculation and used to determine the newly-recalculated spin lock value is: contention on a run queue of an OS scheduler of the multithreaded system.
5. The method of claim 1 , wherein the current environment which is observed by the spin-lock-re-calculation and used to determine the newly-recalculated spin lock value is: load on the multithreaded system as measured by actual number of events currently on all event queues internal to all threads currently in the multithreaded system; actual number of currently runnable contexts in the multithreaded system; and moving average of time taken to signal another thread.
6. The method of claim 1 , wherein the spin-lock-re-calculation that is executed to provide the current spin lock value is executed on a dedicated thread.
7. A computer that provides a tuned spin count in a multithreaded system, comprising:
a memory, which is configured to store a current spin lock value; and
a processor cooperatively operable with the memory, and configured to:
determine a re-calculation time interval at which to re-calculate a current spin lock value;
repeatedly execute, at the re-calculation time interval, a spin-lock-re-calculation that:
observes a current environment of the multithreaded system,
determines, using a second-order tuning and values of the current environment, a dynamically calculated heuristic to provide the newly-recalculated spin lock value, and
memorizes the newly re-calculated spin lock value in the memory as the current spin lock value; and
obtain in at least one thread, the current spin lock value which is in the memory, and executing a spin lock in the at least one thread using the current spin lock value to set a length of the spin lock.
8. The computer of claim 7 , wherein the processor is further configured that the re-calculation time interval at which the spin-lock-re-calculation is executed to observe the current environment is calculated as a constant ratio of a signal call time.
9. The computer of claim 7 , wherein the processor is further configured that the re-calculation time interval is determined using a first-order tuning which uses an exponentially weighted moving average (EWMA) of time taken to signal another thread.
10. The computer of claim 7 , wherein the processor is further configured that the current environment which is observed by the spin-lock-re-calculation and used to determine the newly-recalculated spin lock value is: contention on a run queue of an OS scheduler of the multithreaded system.
11. The computer of claim 7 , wherein the processor is further configured that the current environment which is observed by the spin-lock-re-calculation and used to determine the newly-recalculated spin lock value is: load on the multithreaded system as measured by actual number of events currently on all event queues internal to all threads currently in the multithreaded system; actual number of currently runnable contexts in the multithreaded system; and moving average of time taken to signal another thread.
12. The computer of claim 7 , wherein the processor is further configured that the spin-lock-re-calculation that is executed to provide the current spin lock value is executed on a dedicated thread.
13. A non-transitory computer readable medium comprising executable instructions for a method for a tuned spin count in a multithreaded system, the instructions being executed by a processor to perform:
determining a re-calculation time interval at which to re-calculate a current spin lock value;
repeatedly executing, at the re-calculation time interval, a spin-lock-re-calculation that performs steps of:
observing a current environment of the multithreaded system,
determining, using a second-order tuning and values of the current environment, a dynamically calculated heuristic to provide the newly-recalculated spin lock value, and
memorizing the newly re-calculated spin lock value, in a memory cooperatively operable with the processor, as the current spin lock value; and
obtaining, in at least one thread, the current spin lock value which is memorized in the memory, and executing a spin lock in the at least one thread using the current spin lock value to set a length of the spin lock.
14. The non-transitory computer readable medium of claim 13 , wherein the re-calculation time interval at which the spin-lock-re-calculation is executed to observe the current environment is calculated as a constant ratio of a signal call time.
15. The non-transitory computer readable medium of claim 13 , wherein the re-calculation time interval is determined using a first-order tuning which uses an exponentially weighted moving average (EWMA) of time taken to signal another thread.
16. The non-transitory computer readable medium of claim 13 , wherein the current environment which is observed by the spin-lock-re-calculation and used to determine the newly-recalculated spin lock value is: contention on a run queue of an OS scheduler of the multithreaded system.
17. The non-transitory computer readable medium of claim 13 , wherein the current environment which is observed by the spin-lock-re-calculation and used to determine the newly-recalculated spin lock value is: load on the multithreaded system as measured by actual number of events currently on all event queues internal to all threads currently in the multithreaded system; actual number of currently runnable contexts in the multithreaded system; and moving average of time taken to signal another thread.
18. The non-transitory computer readable medium of claim 13 , wherein the spin-lock-re-calculation that is executed to provide the current spin lock value is executed on a dedicated thread.