The purpose and implementation of cond_resched()

From: Dong Feng
Date: Wed Feb 21 2007 - 11:14:04 EST

I have a question about cond_resched().

What is the condition under which I should invoke cond_resched() irreplaceably?

For example, I see the following code in ksoftirqd(),


But I do not understand why I should not write the following code,


Are the above two pieces of code equal in functionality?

On the other hand, I see cond_resched() check and set PREEMPT_ACTIVE.
I currently do not understand why it should do this, since I think
PREEMPT_ACTIVE is only used to be set in the return-from-interrupt
code in order to prevent schedule() from removing task from run queue
unpredictably. But for cond_resched(), which is a planned voluntary
switch, why does it also deal with this flag?
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at