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MEDIUM: move the ring's lock to only protect the readers list

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Now the lock is only taken around the readers list. With careful
ordering of writes to head/tail, the ring remains protected.

The perf is a bit better, though (1.54M msg/s vs 1.4M at 48T on
a 3rd gen EPYC, and 5.4M vs 5.3M for a 3C6T setup).
This commit is contained in:
Willy Tarreau 2024-02-28 09:52:55 +01:00
parent eb3d5f464d
commit 3cdd3d27a8
1 changed files with 4 additions and 8 deletions
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12
src/ring.c
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@ -245,9 +245,7 @@ ssize_t ring_write(struct ring *ring, size_t maxlen, const struct ist pfx[], siz
pl_wait_unlock_long(&ring->storage->tail, RING_TAIL_LOCK);
}
HA_RWLOCK_WRLOCK(RING_LOCK, &ring->lock);
head_ofs = ring->storage->head;
head_ofs = HA_ATOMIC_LOAD(&ring->storage->head);
/* this is the byte before tail, it contains the users count */
lock_ptr = (uint8_t*)ring_area + (tail_ofs > 0 ? tail_ofs - 1 : ring_size - 1);
@ -329,11 +327,12 @@ ssize_t ring_write(struct ring *ring, size_t maxlen, const struct ist pfx[], siz
/* notify potential readers */
if (sent) {
HA_RWLOCK_RDLOCK(RING_LOCK, &ring->lock);
list_for_each_entry(appctx, &ring->waiters, wait_entry)
appctx_wakeup(appctx);
HA_RWLOCK_RDUNLOCK(RING_LOCK, &ring->lock);
}
HA_RWLOCK_WRUNLOCK(RING_LOCK, &ring->lock);
leave:
return sent;
}
@ -435,10 +434,8 @@ int ring_dispatch_messages(struct ring *ring, void *ctx, size_t *ofs_ptr, size_t
ring_area = (uint8_t *)ring->storage->area;
ring_size = ring->storage->size;
HA_RWLOCK_RDLOCK(RING_LOCK, &ring->lock);
head_ofs = ring_head(ring);
tail_ofs = ring_tail(ring);
head_ofs = HA_ATOMIC_LOAD(&ring->storage->head);
/* explanation for the initialization below: it would be better to do
* this in the parsing function but this would occasionally result in
@ -528,7 +525,6 @@ int ring_dispatch_messages(struct ring *ring, void *ctx, size_t *ofs_ptr, size_t
if (last_ofs_ptr)
*last_ofs_ptr = tail_ofs;
*ofs_ptr = head_ofs;
HA_RWLOCK_RDUNLOCK(RING_LOCK, &ring->lock);
return ret;
}