Subject: [RFC PATCH 3/3] ixgbe: bulk free SKBs during TX completion cleanup cycle

From: Jesper Dangaard Brouer <[email-masked]>
Date: Fri, 04 Sep 2015 19:01:21 +0200

First user of the SKB bulk free API (namely kfree_skb_bulk() via
waitlist helper add-and-flush API).

There is an opportunity to bulk free SKBs during reclaiming of
resources after DMA transmit completes in ixgbe_clean_tx_irq.  Thus,
bulk freeing at this point does not introduce any added latency.
Choosing bulk size 32 even-though budget usually is 64, due (1) to
limit the stack usage and (2) as SLAB behind SKBs have 32 objects per
slab.

Signed-off-by: Jesper Dangaard Brouer <[email-masked]>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 463ff47200f1..d35d6b47bae2 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -1075,6 +1075,7 @@ static void ixgbe_tx_timeout_reset(struct ixgbe_adapter *adapter)
  * @q_vector: structure containing interrupt and ring information
  * @tx_ring: tx ring to clean
  **/
+#define BULK_FREE_SIZE 32
 static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector *q_vector,
 			       struct ixgbe_ring *tx_ring)
 {
@@ -1084,6 +1085,11 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector *q_vector,
 	unsigned int total_bytes = 0, total_packets = 0;
 	unsigned int budget = q_vector->tx.work_limit;
 	unsigned int i = tx_ring->next_to_clean;
+	struct sk_buff *skbs[BULK_FREE_SIZE];
+	struct dev_free_waitlist wl;
+
+	wl.skb_cnt = 0;
+	wl.skbs = skbs;
 
 	if (test_bit(__IXGBE_DOWN, &adapter->state))
 		return true;
@@ -1113,8 +1119,8 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector *q_vector,
 		total_bytes += tx_buffer->bytecount;
 		total_packets += tx_buffer->gso_segs;
 
-		/* free the skb */
-		dev_consume_skb_any(tx_buffer->skb);
+		/* delay skb free and bulk free later */
+		dev_free_waitlist_add(&wl, tx_buffer->skb, BULK_FREE_SIZE);
 
 		/* unmap skb header data */
 		dma_unmap_single(tx_ring->dev,
@@ -1164,6 +1170,8 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector *q_vector,
 		budget--;
 	} while (likely(budget));
 
+	dev_free_waitlist_flush(&wl); /* free remaining SKBs on waitlist */
+
 	i += tx_ring->count;
 	tx_ring->next_to_clean = i;
 	u64_stats_update_begin(&tx_ring->syncp);
@@ -1224,6 +1232,7 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector *q_vector,
 
 	return !!budget;
 }
+#undef BULK_FREE_SIZE
 
 #ifdef CONFIG_IXGBE_DCA
 static void ixgbe_update_tx_dca(struct ixgbe_adapter *adapter,

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