How do I determine if a task is i real-time task in schedule()?

Hi, I'm currently working with a custom scheduler in linux kernel 2.6.23.9. Or actually I'm porting a scheduler I all ready made in Solaris, anyway in sched.c in the schedule() function, I need to determine if a task is a real-time task or not, what is the best way to do this? Do real-time tasks got any flag set that I can check?

Also a question about jiffies, how many ns is a jiffy?

This macro, in sched.c says:

Code:

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#define NS_TO_JIFFIES(TIME) ((TIME) / (1000000000 / HZ))

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But where is HZ set? What is the default value?

Thanks.

d'oh!

Found it: task_has_rt_policy(); ....

Still question about jiffies remains.

HZ - This is the number of hardware clock interrupts per second. This is a "ticks per second" value (T/s).

jiffies / jiffies_64 - These are basically counters that get incremented ever clock interrupt. So this is a "ticks" value (T).

There are 1000 milliseconds (ms) in a second - and 1,000,000 nanoseconds (ns) in a millisecond.

So 1000000000 is the number of nanoseconds in a second - divide by HZ and you now have a value that represents the "nanoseconds per tick" (ns/T). "TIME" in the macro represents a "ns" value, so when you divide "ns ÷ (ns/T)" you end up with just a "T" value - which is ticks or jiffies.

So now that that's out of the way, to your question :)
>> But where is HZ set? What is the default value?

Linux Device Drivers, Third Edition: http://lwn.net/Kernel/LDD3/
You can jump straight to chapter 7 where those questions are answered.

gg