NAME
sysv_hash_locks — System V IPC hashed spinlock pool size
VALUES
Allowed values
Minimum: 64
Maximum: 32768
or
semmni
whichever is smaller.
Required to be a power of two.
DESCRIPTION
The
sysv_hash_locks
tunable specifies the size of the hashed spinlock (kernel data
structures used for synchronization) pool (number of available
spinlocks).
The System V IPC semaphore functions acquire hashed spinlocks based
on the semaphore ID.
The spinlocks are hashed to avoid the memory user needed for
semmni
spinlocks but to also avoid the contention of having just one spinlock.
For more information about System V semaphores, refer to the
"Overview" section of the
sema(5)
manpage.
Who Is Expected to Change This Tunable?
Those who have identified, through kernel performance analysis,
local system performance issues with these locks.
HP experience is that very few customers need to adjust this tunable.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
When Should the Value of This Tunable Be Raised?
This tunable should be raised if performance analysis shows
high contention on these locks.
This could happen as a result of a very large increase to the
semmni
tunable, coupled with very heavy use of semaphore operations.
When Should the Value of This Tunable Be Lowered?
If
semmni
is no longer as large, and/or spinlock contention is no longer an issue.
What Other Tunable Values Should Be Changed at the Same Time?
All the System V semaphore tunables are interrelated and should
not
be treated as independent variables.
The tunables must be evaluated as a system to ensure they reflect the
application requirements.
The
sema
tunables include
semaem,
semmap,
semmni,
semmns,
semmnu,
semmsl,
semume,
semvmx,
and
sysv_hash_locks.
Specifically, significant changes in the number of semaphore IDs via the
semmni
tunable may require changes in the
sysv_hash_locks
tunable.
WARNINGS
All HP-UX kernel tunable parameters are release specific.
This parameter may be removed or have its meaning changed in
future releases of HP-UX.
AUTHOR
sysv_hash_locks
was developed by AT&T.
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