29 Jul
2004
29 Jul
'04
4:51 p.m.
On Thu, Jul 29, 2004 at 08:21:10PM +0200, Ingo Molnar wrote:
* Scott Wood <scott(a)timesys.com> wrote:
ok, i see - this makes 100% sense. I'm wondering how intrusive such an
all-preemptive patchset is? There are some problems with per-CPU data
structures on SMP. Right now holding a spinlock means one can use
smp_processor_id() and rely on it staying constant in the critical
section. With a mutex in the same place all such assumptions would
break. Is there some automatic way to deal with these issues (or to at
least detect them reliably?).
Make smp_processor_id check if preempt_count() is non-zero to make sure
that you're running within a non-preemptable critical section (scheduler
deferred). Do the same with local_irq_* critical section by checking to
see if interrupts are disabled. They are also non-preemptable (hardware
defered).
That's my suggestion.
bill