preemptible kernel patch

Adding the preemption patches will not make it any faster, and, in fact, will slightly degrade application throughput.

Right. A real time application is one where the time it takes to get the answer is as important as the answer. It doesn't have to be fast, just very predictable.

You run your application before and after. If your application can't see the difference, you don't need the preemption patches.

What are you seeing with your application (and what is your application?) that makes you think the preemption patches will help?

If you are intending that anyway, you should try Kernel 2.6, as the preemption is already present there.

Kernel preemption only helps high priority tasks to more likely meet time constrains.

So you at first would run your application with "realtime priority" to schedule it before any time-sliced applications.

-Michael

MontaVista has backported it to 2.4, so it should be fairly easy to insert it there as well. I am not sure however where you can download the patch.

Freddy

Thanks Steve,

My application is a video capturing application running with Linux BTTV and reading some custom I/O, Network data transfer and few more things. basically i am doing around 4-5 major tasks simultaneously in different child processes.

Now with frame capturing if i try to do many tasks simultaneously it drops the frame capture rate so the quality of the video drops down, so if i improve the performance by preemptive patch of the system and ask the system to go and capture the frame as a top priority task, i might able to get faster frame rate with all other task i am handling.

Any suggestions ??? What do you say ???

Thanks

Rushi steve@nos

First:

Do you know where frames get dropped? Do you send the images over network? Using UDP? ...

Second:

Video - 25-30 frames / second or something like that? At least two buffers (ping pong) would give you 1/30 second to move the frame. That is more than ten milli seconds - should almost be possible without preemption...

So have you made the time critical process RT (SCHED_RR or SCHED_FIFO) with 'sched_setscheduler(pid, SCHED_RR, param)' BTW do not use maximum, use lowest... there are probably no other RT processes running in your system...

/RogerL

Great Roger,

Erectly what i was looking for , you are right i am not doing any time critical processes. I do continues recording in background and than do lots of other tasks like reading the I/Os , deleting the previous recording, transferring the data over the socket, and scanning few other system variables.

If i start doing any of this processes in parallel with frame capturing from memory ( ya i am using two buffers) capturing drops down to less frames per second.

But if I schedule the PID of capturing process to higher priority (as you have mentioned), i am sure it will make lot of different.

Let me try it tomorrow....

Thanks