On Wed, 2002-07-24 at 17:45, Andrew Morton wrote:
> Robert Love wrote:
> >
> > +static inline void cond_resched_lock(spinlock_t * lock)
> > +{
> > + if (need_resched() && preempt_count() == 1) {
> > + _raw_spin_unlock(lock);
> > + preempt_enable_no_resched();
> > + __cond_resched();
> > + spin_lock(lock);
> > + }
> > +}
>
> Maybe I'm being thick. How come a simple spin_unlock() in here
> won't do the right thing?
It will, but we will check need_resched twice. And preempt_count
again. My original version just did the "unlock; lock" combo and thus
the checking was automatic... but if we want to check before we unlock,
we might as well be optimal about it.
> And this won't _really_ compile to nothing with CONFIG_PREEMPT=n,
> will it? It just does nothing because preempt_count() is zero?
I hope it compiles to nothing! There is a false in an if... oh, wait,
to preserve possible side-effects gcc will keep the need_resched() call
so I guess we should reorder it as:
if (preempt_count() == 1 && need_resched())
Then we get "if (0 && ..)" which should hopefully be evaluated away.
Then the inline is empty and nothing need be done.
Robert Love
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This archive was generated by hypermail 2b29 : Tue Jul 30 2002 - 14:00:18 EST