[Xen-devel] Scheduler guts question

["Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>]

I'm trying to track down a problem on Xen/ia64 and to help
find it, I need to better understand the common scheduler
code and probably the Xen/x86 implementation.  The question
is: What forces a domain to give up the CPU?

At a high-level, it probably works something like this:

1) A timer interrupt occurs which causes an interrupt
   handler (do_IRQ()->timer_interrupt()?) to be launched.
2) Some counter is incremented
3) The counter exceeds some threshold which results in
   some routine being called which "evicts" the currently
   running domain (or in -unstable the running exec_domain).
4) The scheduler is called (__enter_scheduler()?) which
   looks at a queue to determine what tasks are runnable
   and chooses one and launches it.

Looking at the code, I am missing some key connection
between the interrupt routines and the scheduler routines.
Perhaps there is some hidden call in a macro or in
a function pointer indirection that I am missing.

Could someone walk me through at a low level the sequence
of Xen/x86 calls that occur when a timer interrupt results in
some timer expiration that results in the currently running
domain getting "paused" and another domain launched?

Thanks for any help!
Dan


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