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    SubjectRe: [(RT RFC) PATCH v2 5/9] adaptive real-time lock support
    Hi!

    > +/*
    > + * Adaptive-rtlocks will busywait when possible, and sleep only if
    > + * necessary. Note that the busyloop looks racy, and it is....but we do
    > + * not care. If we lose any races it simply means that we spin one more
    > + * time before seeing that we need to break-out on the next iteration.
    > + *
    > + * We realize this is a relatively large function to inline, but note that
    > + * it is only instantiated 1 or 2 times max, and it makes a measurable
    > + * performance different to avoid the call.
    > + *
    > + * Returns 1 if we should sleep
    > + *
    > + */
    > +static inline int
    > +adaptive_wait(struct rt_mutex *lock, struct rt_mutex_waiter *waiter,
    > + struct adaptive_waiter *adaptive)
    > +{
    > + int sleep = 0;
    > +
    > + for (;;) {
    > + /*
    > + * If the task was re-awoken, break out completely so we can
    > + * reloop through the lock-acquisition code.
    > + */
    > + if (!waiter->task)
    > + break;
    > +
    > + /*
    > + * We need to break if the owner changed so we can reloop
    > + * and safely acquire the owner-pointer again with the
    > + * wait_lock held.
    > + */
    > + if (adaptive->owner != rt_mutex_owner(lock))
    > + break;
    > +
    > + /*
    > + * If we got here, presumably the lock ownership is still
    > + * current. We will use it to our advantage to be able to
    > + * spin without disabling preemption...
    > + */
    > +
    > + /*
    > + * .. sleep if the owner is not running..
    > + */
    > + if (!adaptive->owner->se.on_rq) {
    > + sleep = 1;
    > + break;
    > + }
    > +
    > + /*
    > + * .. or is running on our own cpu (to prevent deadlock)
    > + */
    > + if (task_cpu(adaptive->owner) == task_cpu(current)) {
    > + sleep = 1;
    > + break;
    > + }
    > +
    > + cpu_relax();
    > + }
    > +
    > + put_task_struct(adaptive->owner);
    > +
    > + return sleep;
    > +}
    > +

    You want to inline this?

    > +static inline void
    > +prepare_adaptive_wait(struct rt_mutex *lock, struct adaptive_waiter *adaptive)
    ...
    > +#define prepare_adaptive_wait(lock, busy) {}

    This is evil. Use empty inline function instead (same for the other
    function, there you can maybe get away with it).
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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