Hi Ratheesh, I ll give a try.
On Wed, Apr 17, 2013 at 9:43 PM, ratheesh kannoth <[email protected]>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 > > _______________________________________________ > Kernelnewbies mailing list > [email protected] > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >
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