Re: scheduler/SCHED_FIFO behaviour

[Florian Schmidt <mista.tapas@gmx.net>]

On Mon, 02 May 2005 10:57:29 +0530
"Arun Srinivas" <getarunsri@hotmail.com> wrote:

> 1) From main(i.e., parent) create a shared memory seg. using shmget() and 
> shmat(). This is for communication between parent and child. I am trying to 
> use this as a locking mechanism to make them tightly coupled so that one 
> does not race before the other.
> 2) create child by fork() and call shmat() to attach this segment to child 
> too
> 3) In parent and child call ioctl() to pass their PID's from user space to 
> kernel space...so that I can measure when the particular PID's are scheduled 
> in the scheduler
> 
> I suppose shmget() dosent use a system call.So still confused about the 
> occasional resechedule behavior.

You might try the user triggered tracing which is available with Ingo's
realtime preemption patches.

Enable the latency tracing in the kernel confgig and 

echo 1 > /proc/sys/kernel/user_triggered_tracing

then in your code you want to be checked do this before the section:

gettimeofday (1, 1)

and

gettimeofday (1, 0)

after the section you want to be checked.. Every reschedule of the task
will result in a signal SIGUSR2 sent to your program and a latency trace
in the syslog..

..i think

Flo


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