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rcu: simplify memory barriers
Thanks to the acquire semantics of qemu_event_reset and qemu_event_wait, some memory barriers can be removed. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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parent
374293ca6f
commit
e11131b025
11
util/rcu.c
11
util/rcu.c
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@ -82,14 +82,16 @@ static void wait_for_readers(void)
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/* Instead of using atomic_mb_set for index->waiting, and
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* atomic_mb_read for index->ctr, memory barriers are placed
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* manually since writes to different threads are independent.
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* atomic_mb_set has a smp_wmb before...
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* qemu_event_reset has acquire semantics, so no memory barrier
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* is needed here.
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*/
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smp_wmb();
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QLIST_FOREACH(index, ®istry, node) {
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atomic_set(&index->waiting, true);
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}
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/* ... and a smp_mb after. */
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/* Here, order the stores to index->waiting before the
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* loads of index->ctr.
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*/
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smp_mb();
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QLIST_FOREACH_SAFE(index, ®istry, node, tmp) {
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@ -104,9 +106,6 @@ static void wait_for_readers(void)
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}
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}
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/* atomic_mb_read has smp_rmb after. */
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smp_rmb();
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if (QLIST_EMPTY(®istry)) {
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break;
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}
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