Re: [PATCH 3/4] locking: Introduce smp_cond_acquire()

[Davidlohr Bueso <dave@stgolabs.net>]

On Thu, 03 Dec 2015, Peter Zijlstra wrote:

>+/**
>+ * smp_cond_acquire() - Spin wait for cond with ACQUIRE ordering
>+ * @cond: boolean expression to wait for
>+ *
>+ * Equivalent to using smp_load_acquire() on the condition variable but employs
>+ * the control dependency of the wait to reduce the barrier on many platforms.
>+ *
>+ * The control dependency provides a LOAD->STORE order, the additional RMB
>+ * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
>+ * aka. ACQUIRE.
>+ */
>+#define smp_cond_acquire(cond)	do {		\
>+	while (!(cond))				\
>+		cpu_relax();			\
>+	smp_rmb(); /* ctrl + rmb := acquire */	\
>+} while (0)

So this hides the fact that we actually are waiting on the cond, as opposed
to conditional acquiring. Could it be renamed to something like smp_waitcond_acquire()?

Thanks,
Davidlohr