Messages in this thread | | | Date | Tue, 5 Jul 2022 19:34:25 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 12/13] locking/qspinlock: separate pv_wait_node from the non-paravirt path |
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On Tue, Jul 05, 2022 at 12:38:19AM +1000, Nicholas Piggin wrote: > pv_wait_node waits until node->locked is non-zero, no need for the > pv case to wait again by also executing the !pv code path. > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com> > --- > kernel/locking/qspinlock.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index 9db168753124..19e2f286be0a 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -862,10 +862,11 @@ static inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, bool parav > /* Link @node into the waitqueue. */ > WRITE_ONCE(prev->next, node); > > + /* Wait for mcs node lock to be released */ > if (paravirt) > pv_wait_node(node, prev); > - /* Wait for mcs node lock to be released */ > - smp_cond_load_acquire(&node->locked, VAL); > + else > + smp_cond_load_acquire(&node->locked, VAL); >
(from patch #6):
+static void pv_wait_node(struct qnode *node, struct qnode *prev) +{ + int loop; + bool wait_early; + ... + + /* + * By now our node->locked should be 1 and our caller will not actually + * spin-wait for it. We do however rely on our caller to do a + * load-acquire for us. + */ +}
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