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Full Discussion: semaphore access speed
Top Forums Programming semaphore access speed Post 302245538 by otheus on Friday 10th of October 2008 10:07:07 AM
Old 10-10-2008
SemOp Benchmarks on various Linux servers

I have run benchmarks on the following hardware:
  • Xeon 3600, 1024k Cache, no SEP, no model #
  • Xeon 2800, 512k Cache, no SEP, no model #
  • Xeon 2333, 4095k Cache, no SEP, E5E45
  • Opteron 1000, 1024k Cache, no SEP, 270
  • Opteron 2000, 1024k Cache, SEP, 270
  • Opteron 2600, 1024k Cache, no SEP, 285
  • Opteron 2600, 1024k Cache, SEP, 285
These systems were under various amounts of load, so averages were taken, and they cannot be deemed 100% reliable. The benchmarks used a gettimeofday() call which looped for at least 3 seconds. The attached PDFs shows the results in terms of "Tics per SemOp". and "SemOps per Second".

Observations:
The Opteron 270 running at 1GHz and using int 80 for system calls was the fastest per clock tic. The fastest processors (the Xeons) were the slowest. This suggests the problem is the memory access.

The raw numbers show that the sysent call on the Opteron makes the semop about 14% faster. Static compilation generally improved speeds, though because of system load, I would not put much significance on these numbers. The only dynamic linking, really, is the library call to invoke a system call.

Analysis:
I'm going to leave it to others to explain this data.
 

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event_class(5)															    event_class(5)

NAME
event class file - The file that contains the declaration of an event class. DESCRIPTION
Audit events can be logically grouped into event classes. Event classes are defined in event class files. An event class file contains an event class number and a list of event numbers corresponding to audit events. All event class files must be created in the dcelocal/etc/audit/ec directory. The name of the event class file becomes the name of the event class. The recommended naming convention for event class files is: dce_server-name_class where class is a descriptive text that characterizes the event class. Event class files must be write-protected by the local operating system (that is, only administrators should have write access to these files). Audit clients read these files to maintain an event table in their address space. Optionally, an event class file can contain a SEP line. This line contains a list of prefixes of the event numbers in the file. The SEP line speeds up the scanning performed by the Audit clients. Audit clients which do not have events with one of the prefixes listed will not scan the event list. If the SEP line is not provided in the file, Audit clients will have to read the entire file to find out if the event class file contains any of their events. Empty lines are ignored in the event class file. Comments are designated by the number sign (#) placed before the comment text. The Event Class File Format The format of an event class file is: ECN=event_class_number SEP=prefix_1 prefix_2 ... # comments start with the number sign event_num- ber_1 event_number_2 EXAMPLES
Following is an example of an event class file for the event class ec_local_authentication: ECN = 0x00000001 SEP = 0x100 # AS_Request 0x00000100 # TGS_TicketReq 0x00000101 # TGS_RenewReq 0x00000102 # TGS_ValidateReq 0x00000103 event_class(5)
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