05-13-2010
The performance critical cpmpeting process ...
For example the bottom half implementation of any Linux driver code need to use the spinlock instead of mutex (or any seamaphores for that maters), otherwise contex switch in seamaphore based synchronization proves to be too expensive. However, there is also some pitfalls associated with spinlock based implementations (specially any application going to be used as server and need to handle high connection rates should avoid spinlock() ).
Please look at the Rubini's Linux Device Driver ebook for a better and a detailed discussion.
This User Gave Thanks to Praveen_218 For This Post:
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LEARN ABOUT HPUX
sysv_hash_locks
sysv_hash_locks(5) File Formats Manual sysv_hash_locks(5)
NAME
sysv_hash_locks - System V IPC hashed spinlock pool size
VALUES
Failsafe
Default
Allowed values
or whichever is smaller.
Required to be a power of two.
DESCRIPTION
Note: If the DynSysVSem optional product bundle is installed then this tunable is ignored and has no effect. Each semaphore ID has a sep-
arate lock.
The tunable specifies the size of the hashed spinlock (kernel data structures used for synchronization) pool (number of available spin-
locks). 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 spinlocks but to also avoid the contention of having just one spinlock.
For more information about System V semaphores, refer to the 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.
Note: If the DynSysVSem optional product bundle is installed then changes to this tunable are ignored and have no effect.
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 tunable, coupled with very heavy use of semaphore operations.
When Should the Value of This Tunable Be Lowered?
If 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 semaphore tunables include and Specifically, significant changes in the
number of semaphore IDs via the tunable may require changes in the tunable.
Note: If the DynSysVSem optional product bundle is installed then the and tunables are ignored and have no effect.
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.
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 tun-
able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was
factory installed on your system, see at
AUTHOR
was developed by AT&T.
SEE ALSO
sema(5), semaem(5), semmni(5), semmns(5), semmnu(5), semmsl(5), semume(5), semvmx(5).
Tunable Kernel Parameters sysv_hash_locks(5)