On Wed, Oct 7, 2009 at 1:57 PM, er krishna <erkrishna@xxxxxxxxx> wrote: > > > On Wed, Oct 7, 2009 at 12:45 PM, govind raj nayak <govind02@xxxxxxxxxxxxxx> wrote: >> >> Yes, spinlock would automatically disable kernel preemption. > > >>>>>>I don't think so, otherwise what is the use of spin_lock_irq_save api, if spin_lock api does it ?. I mean if spin_lock api >>>>>>is disabling the kernel preemption, then can a newly occured interrupt will preempt currently executing process which >>>>>>has taken a spin lock by spin_lock() api. Just confirm my understanding. > > >>>>>>>I don't think all the spinlock api will disable kernel preemption. We must check in kernel code, that on which API >>>>>>>preemption is disable or if anybody knows, please mention those ones. > > >> >> I was just giving theeoritical overview. As far as I know not all synchronization constructs would disable the kernel preemption > > >>>>>>Yes, agreed. > >>>>>>Can we say if preemption is disable but interrupts are not, then interrupt handler won't be able to preempt the currently executing process. > > >>>>>> I am just asking, if we have disable the interrupts on local processor by some api, and suddenly if higher priority >>>>>> process/ interrupt comes (the first process which is currently executing has acquired a spin lock by >>>>>>spin_lock_irq_save() api). I just want to know weather the higher priority process/interrupt will preempt the lower priority >>>>>> process or it will spin. > > > Just clear the confusion. > > > Regards, > Krishna > >> >> automatically (for instance when acquiring a big kernel lock). In addition you could use preempt_enable() and preempt_disable() to explicitly enable or disable kernel preemption. Thanks. >> >> -Govindraj >> >> On Wed, 07 Oct 2009 11:15:06 +0530 wrote >> >Rajat San,Just asking (since i didn't see spinlock implementation in kernel src),On Tue, Oct 6, 2009 at 5:52 PM, Rajat Jain wrote: >> >> Hello Govind, >> >> > What happens when you go for spin locks without >> > disabling kernel preemption? Suppose you acquire >> > a spin lock in a system call handler (a service >> > routine on behalf of a user mode process) with >> > kernel preemption enabled. >> >> This is not possible. Spin lock APIs disable kernel preemption >> automatically.Spin lock APIs disables kernel preemption in all its api or some specific apis only. Please confirm and elaborate. >> >> >> Thanks, >> >> RajatBest regards,Krishna >> > Krishna, you seem to be getting confused between kernel getting preempted and kernel getting interrupted. Any spin lock will disable kernel preemption. If you use spin_lock() then it will just disable kernel preemption but if you get any interrupt then its handler will get executed. But if you use spin_lock_irqsave() then it will disable preemption plus it will disable local interrupts. I suggest you should read "Kernel Synchronization Methods" chapter from Linux Kernel Development by Robert Love. -Vinit -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
