Applications that consume a batch of entries in one go
can benefit from ability to return some of them back
into the ring.
Add an API for that - assuming there's space. If there's no space
naturally can't do this and have to drop entries, but this implies ring
is full so we'd likely drop some anyway.
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
Jason, if you add this and unconsume the outstanding packets
on backend disconnect, vhost close and reset, I think
we should apply your patch even if we don't yet know 100%
why it helps.
changes from v1:
- fix up coding style issues reported by Sergei Shtylyov
include/linux/ptr_ring.h | 56 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 56 insertions(+)
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 783e7f5..902afc2 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -457,6 +457,62 @@ static inline int ptr_ring_init(struct ptr_ring *r, int
size, gfp_t gfp)
return 0;
}
+/*
+ * Return entries into ring. Destroy entries that don't fit.
+ *
+ * Note: this is expected to be a rare slow path operation.
+ *
+ * Note: producer lock is nested within consumer lock, so if you
+ * resize you must make sure all uses nest correctly.
+ * In particular if you consume ring in interrupt or BH context, you must
+ * disable interrupts/BH when doing so.
+ */
+static inline void ptr_ring_unconsume(struct ptr_ring *r, void **batch, int n,
+ void (*destroy)(void *))
+{
+ unsigned long flags;
+ int head;
+
+ spin_lock_irqsave(&r->consumer_lock, flags);
+ spin_lock(&r->producer_lock);
+
+ if (!r->size)
+ goto done;
+
+ /*
+ * Clean out buffered entries (for simplicity). This way following code
+ * can test entries for NULL and if not assume they are valid.
+ */
+ head = r->consumer_head - 1;
+ while (likely(head >= r->consumer_tail))
+ r->queue[head--] = NULL;
+ r->consumer_tail = r->consumer_head;
+
+ /*
+ * Go over entries in batch, start moving head back and copy entries.
+ * Stop when we run into previously unconsumed entries.
+ */
+ while (n--) {
+ head = r->consumer_head - 1;
+ if (head < 0)
+ head = r->size - 1;
+ if (r->queue[head]) {
+ /* This batch entry will have to be destroyed. */
+ ++n;
+ goto done;
+ }
+ r->queue[head] = batch[n];
+ r->consumer_tail = r->consumer_head = head;
+ }
+
+done:
+ /* Destroy all entries left in the batch. */
+ while (n--)
+ destroy(batch[n]);
+ spin_unlock(&r->producer_lock);
+ spin_unlock_irqrestore(&r->consumer_lock, flags);
+}
+
static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
int size, gfp_t gfp,
void (*destroy)(void *))
--
MST
