about the meaning of the "a real time priority"

[leyearn]

when i read the document of mc/ServiceGuard
the section that describe "Cluster Daemon: cmcld" is :
This daemon is used to determine cluster membership by sending
heartbeat messages to other cmcld daemons on other nodes within the
ServiceGuard cluster. It runs at a real time priority and is locked in
memory. The cmcld daemon sets a safety timer in the kernel which is
used to detect kernel hangs.

what is the meaning of "real time priority "and "safety timer "?

thankS!

[Steven E. Protter · Accepted solution]

Bill Hassel's answer sounds good in this thread.
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xc5fd5dc05a7ad711abdc0090277a778c,00.html

This thread may do it for safety timers.
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xaf005f938a10d6118ff40090279cd0f9,00.html

Page 33 of this doc does both. Its a Linux doc though, so I'd be somewhat wary.
http://docs.hp.com/linux/pdf/B9903-90005.pdf

Obviously I don't know the answer, or I'd just past in the definitions out of my head. I made this post so you don't have to wait. It might actually contain the answer.

SEP

[T G Manikandan]

There are different priorities for a process

Real time processes (RT)
System Processes
Timesharing processes

Real time processes have the highest priority on the system.They respond to external events as they happen.
No other processes can be serviced while a real-time process has control of the CPU.

[Sridhar Bhaskarla]

Hi,

There are two types of priorities that can be set to a process. Time sharing or real time. Again there are priorities within these classes depending on the priority value . Real-time processes continously run unless they wait for IO or sleep. It could also give away to a high priority process. A pure cpu bound high priority real time process can cause the CPU to be unavaible to other processes.

Safety timer is a mechanism by which kernel can detect the cmcld hangups and perform a TOC on the system to prevent data corruption. One of the jobs of cmcld is to reset the safety timer time to time. If any hangs prevents it from doing so, kernel will detect it and issues a TOC.

-Sri