I ll give a try.
On Wed, Apr 17, 2013 at 9:43 PM, ratheesh kannoth <ratheesh.ksz@xxxxxxxxx> wrote:
I would like to understand on linux scheduler context. I have read a
lot in websites and i could find
contradictory statement. There are so many mailing list also ,but with
less info. I would really appreciate
if anybody could spend some time answering my question.
1. Which context scheduler run ? ( process context or interrupt context ).
Process context. That is when preempt_count equal 0
2. scheduler is the guy who picks up the next candidate to run. if
it gets interrupted by hardirq, what will happen ?
scheduler resumes from where it was stopped, after finishing hardirq handler(and softirq handlers if any)
3. if scheduler run in process context , how bottom half are scheduled ?
Bottom halves(softirqs and tasklets) are not scheduled by scheduler.
ISR is executed in_irq() context or with preempt count added with HARDIRQ_OFFSET.
Local interrupts are disabled in_irq() context.
After completing ISR, irq_exit() function checks for any pending softirqs, if yes it invokes invoke_softirq() to service all pending softirqs with interrrupts enabled.
When softirqs runs, preempt count will be added with SOFTIRQ_OFFSET.
4. In smp, schedule() function may be called simultaneously. How it
is handled ?
Each core has its own runqueue which is a per_cpu variable.
5. When a bottom half is interrupted by hard irq, how softirq kernel
thread saves the state and restart it later ? ...what i mean is , an
hardirq came and its isr executed. bottom half enabled and bottom
half gets scheduled . Before bottom half is completed , next irq
came and it enables bottom half , and the new bottom half is
scheduled ....So here , what will happen to old bottom half , will it
again
run later ?
The old bottom half handler(which was preempted by irq) will be resumed after the hardirq isr.
Followed by the next bottom half.
Refer function __do_softirq in kernel/softirq.c
Thanks,
Arun
Thanks,
Ratheesh
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