Re: Interruption and preemption

[Eric BEGOT <eric_begot@xxxxxxxx>]

Nilanjan Roychowdhury wrote:
> -----Original Message-----
> From: kernelnewbies-bounce@xxxxxxxxxxxx [mailto:kernelnewbies-bounce@xxxxxxxxxxxx] On Behalf Of Eric BEGOT
> Sent: Friday, April 30, 2004 8:35 PM
> To: kernelnewbies@xxxxxxxxxxxx
> Subject: Interruption and preemption
>
> Hi all,
> I've some questions about the preemption of the kernel. In the Linux 2.2 
> and 2.4, there are a lot of spin_lock_irqsave to disable interrupt like :
> spin_lock_irqsave() ;
> CRITICAL SECTION
> spin_lock_irqrestore() ;
> In a non preemptive kernel, the critical section is executed as an 
> atomic operation that's sure. But in a preemptive kernel, the kernel can 
> be interrupted by a process. So the kernel has a timeslice and if the 
> timeslice finishes in the CRITICAL section, there's a problem.
>
>
> > > > > > > > if the timeslice finishes then kernel will be notified by a timer >>>>>>>interrupt.But as the interrupts are disbled the process wont get >>>>>>>scheduled inside the CRITICAL section. What do ya say ???
Yes I agree. But if the timeslice of the kernel finishes, then the 
kernel can be replaced by another process. And if in the new current 
process, the structures in the CRITICAL SECTION are accessed to, there 
can be a problem no ?
If it is a completely preemptive kernel.
Of course we don't care of interrupts if interrupts are disabled :)
> And this code in SMP environment doesn't work neither, does it ? It only 
> protects the interrupts of 1 processor no ?
> Just some thoughts about synchronization :)
>
> Thx :p
>
> Eric
>
>
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