|
|
HP-UX Reference > Ppfdat_hash_locks(5)Tunable Kernel ParametersHP-UX 11i Version 2: December 2007 Update |
|
NAMEpfdat_hash_locks — determines the size of the pfdat spinlock pool DESCRIPTIONGlobal kernel structures containing information on a running process or memory usage are frequently accessed or modified by several threads concurrently. To prevent race conditions, these structures are protected by spinlocks (kernel data used for synchronization) which allow only the spinlock "holder" to proceed, while all others attempting to access the structure must wait. Hashed spinlocks are used when each instance of such a data structure is to be protected, and there are several instances. Using a single spinlock for all instances would cause too much contention, but using one spinlock per structure wastes memory while the majority of the locks are unused at any given time. By allocating a pool of hashed locks, a hash function picks one lock per group of structures, reducing contention while conserving memory. This tunable sets the size of such a pool for the pfdat data structure spinlocks. Who Is Expected to Change This Tunable?Only HP Field engineers should change the value of this tunable. When Should the Value of This Tunable Be Raised?This tunable should be raised on systems with both low memory contention and high lock contention due to a large number of pfdat structures. Typically, such a system would be a large memory system with a large amount of processes or threads. When Should the Value of This Tunable Be Lowered?This tunable should only be lowered on systems with high contention for physical memory and few processes and threads. The memory saved by making the table smaller will be freed for general use, and could cause contention if many pfdat structures are present and requiring locks. WARNINGSAll HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX. Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tunable values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see HP-UX Release Notes at http://docs.hp.com. |
|