Next: , Previous: , Up: Tunables   [Contents][Index]


37.4 Elision Tunables

Tunable namespace: glibc.elision

Contended locks are usually slow and can lead to performance and scalability issues in multithread code. Lock elision will use memory transactions to under certain conditions, to elide locks and improve performance. Elision behavior can be modified by setting the following tunables in the elision namespace:

Tunable: glibc.elision.enable

The glibc.elision.enable tunable enables lock elision if the feature is supported by the hardware. If elision is not supported by the hardware this tunable has no effect.

Elision tunables are supported for 64-bit Intel, IBM POWER, and z System architectures.

Tunable: glibc.elision.skip_lock_busy

The glibc.elision.skip_lock_busy tunable sets how many times to use a non-transactional lock after a transactional failure has occurred because the lock is already acquired. Expressed in number of lock acquisition attempts.

The default value of this tunable is ‘3’.

Tunable: glibc.elision.skip_lock_internal_abort

The glibc.elision.skip_lock_internal_abort tunable sets how many times the thread should avoid using elision if a transaction aborted for any reason other than a different thread’s memory accesses. Expressed in number of lock acquisition attempts.

The default value of this tunable is ‘3’.

Tunable: glibc.elision.skip_lock_after_retries

The glibc.elision.skip_lock_after_retries tunable sets how many times to try to elide a lock with transactions, that only failed due to a different thread’s memory accesses, before falling back to regular lock. Expressed in number of lock elision attempts.

This tunable is supported only on IBM POWER, and z System architectures.

The default value of this tunable is ‘3’.

Tunable: glibc.elision.tries

The glibc.elision.tries sets how many times to retry elision if there is chance for the transaction to finish execution e.g., it wasn’t aborted due to the lock being already acquired. If elision is not supported by the hardware this tunable is set to ‘0’ to avoid retries.

The default value of this tunable is ‘3’.

Tunable: glibc.elision.skip_trylock_internal_abort

The glibc.elision.skip_trylock_internal_abort tunable sets how many times the thread should avoid trying the lock if a transaction aborted due to reasons other than a different thread’s memory accesses. Expressed in number of try lock attempts.

The default value of this tunable is ‘3’.


Next: , Previous: , Up: Tunables   [Contents][Index]