Re: The purpose and implementation of cond_resched()
I re-checked the code. And this time, I think cond_resched() is useful while a kernel is compiled with no full preemption function but only voluntary kernel preemption is enabled (i.e. CONFIG_PREEMPT_VOLUNTARY is set but CONFIG_PREEMPT is not set). In this case, kernel performs scheduling at explicit voluntary preemption points only, and those points are determined by invoking cond_resched(). But I still have questions, why cond_resched() does not yield no-op while CONFIG_PREEMPT is set? And why does it deal with the PREEMPT_ACTIVE flag anyway? 2007/2/22, Dong Feng <[EMAIL PROTECTED]>: 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(), preempt_enable_no_resched(); cond_resched(); preempt_disable(); But I do not understand why I should not write the following code, preempt_enable(); preempt_disable(); 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
The purpose and implementation of cond_resched()
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(), preempt_enable_no_resched(); cond_resched(); preempt_disable(); But I do not understand why I should not write the following code, preempt_enable(); preempt_disable(); 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
The purpose and implementation of cond_resched()
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(), preempt_enable_no_resched(); cond_resched(); preempt_disable(); But I do not understand why I should not write the following code, preempt_enable(); preempt_disable(); 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: The purpose and implementation of cond_resched()
I re-checked the code. And this time, I think cond_resched() is useful while a kernel is compiled with no full preemption function but only voluntary kernel preemption is enabled (i.e. CONFIG_PREEMPT_VOLUNTARY is set but CONFIG_PREEMPT is not set). In this case, kernel performs scheduling at explicit voluntary preemption points only, and those points are determined by invoking cond_resched(). But I still have questions, why cond_resched() does not yield no-op while CONFIG_PREEMPT is set? And why does it deal with the PREEMPT_ACTIVE flag anyway? 2007/2/22, Dong Feng [EMAIL PROTECTED]: 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(), preempt_enable_no_resched(); cond_resched(); preempt_disable(); But I do not understand why I should not write the following code, preempt_enable(); preempt_disable(); 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/