Re: smp_send_reschedule vs. smp_migrate_task

[Paul Mackerras]

Val Henson writes:

> I had only one IPI for the RPIC (an interrupt controller only used on
> Synergy PPC boards) and I implemented a little message queue to
> simulate all 4 IPI's.  The mailbox implementation suggested by James
> Bottomley ended up having race conditions on our board.  It's probably
> not the most elegant solution, but it works and required no change to
> the PowerPC SMP code.  See my "Make Gemini boot" patch to linuxppc-dev
> and take a look at the files rpic.c and rpic.h.

In that post I was really asking the following questions:

* how often does smp_send_reschedule get called?
* how often does smp_migrate_task get called?
* if smp_send_reschedule and smp_migrate_task were mutually exclusive,
  i.e. both used the same spinlock, could that lead to deadlock?

James Bottomley answered the first two for me but not the third.

Paul.