Thanks for explanation, but is there any delay between interrupt handler and softirq execution. Suppose say INT7 triggered and its handler got executed. Now this handler raised the softirq and finished its interrupt context. Since interrupts preempts the current running task, after finishing IRQ context does the task should resumes. But since softirq was scheduled (raised), then is it that softirq will be executed immediately after interrupt handler or it takes some time when interrupted task was switched out and scheduler recognizes a softirq was pending. I know that ksoftirqd is responsible to execute all pending softirqs , who will invoke this, and for every periodic time ksoftirqd invokes and executes softirq. Can you please explain. Thanks.
Regards,
Sri.
On Thu, Sep 9, 2010 at 9:23 PM, Dave Hylands <dhylands@xxxxxxxxx> wrote:
Hi Sri,
Replying to the list...
On Thu, Sep 9, 2010 at 5:08 PM, Sri Ram Vemulpali wrote:
> Hi,
> Can any one explain, when interrupt handler schedules softirq, for bottom
> half work, when is that softirq is executed. Is it immediately after
> interrupt handler context or after some time later when scheduler was
> invoked.
Softirqs are run with interrupts enabled, and run when all of the
nested irqs have completed. Task switching is suspended while
irqs/softirs are being run.
IRQA occurs
IRQA handler gets called
IRQB occurs, interrupting IRQA (assuming IRQA was setup to allow
itself to be interrupted)
IRQB schedules a softirq
IRQB exits
IRQA continues to run
IRQA exits
we're now in a situation where the IRQ depth is zero, so softirqs are run.
when all softirqs are finished, then regular scheduling of tasks resumes.
> I am trying to understand execution context of BHs. I know that tasklets
> execute at relaxed time when system deems to execute. But what about
> softirq. Since softirq's are in nature high in priority, therefore they
> should run immediately after IRQ. I am trying to understand is there any
> latency between IRQ and softirq execution scheduled by that corresponding
> IRQ. Please can anyone explain the sequence of operations how the softirq is
> recognized (that it was set) and scheduled to execute.
softirqs and tasklets are really the same thing (as far as I know).
They run with interrupts enabled, but preemption disabled.
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