From 197a5212c3dd70be267b5cd930be0fb68bb53018 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Wed, 17 May 2017 12:14:37 +0800 Subject: [PATCH] ptr_ring: add ptr_ring_unconsume 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 Signed-off-by: Jason Wang Signed-off-by: David S. Miller --- include/linux/ptr_ring.h | 55 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h index 6b2e0dd..796b90f 100644 --- a/include/linux/ptr_ring.h +++ b/include/linux/ptr_ring.h @@ -403,6 +403,61 @@ 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. */ + 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 *)) -- 2.7.4