From d38df0d364c3a154065109eb855f8d15ecd0fae2 Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Thu, 27 Apr 2017 21:06:18 -0700 Subject: [PATCH] nfp: avoid reading TX queue indexes from the device Reading TX queue indexes from the device memory on each interrupt is expensive. It's doubly expensive with XDP running since we have two TX rings to check there. If the software indexes indicate that the TX queue is completely empty, however, we don't need to look at the device completion index at all. The queuing CPU is doing a wmb() before kicking the device TX so we should be safe to assume on the CPU handling the completions will never see old value of the software copy of the index. Signed-off-by: Jakub Kicinski Signed-off-by: David S. Miller --- drivers/net/ethernet/netronome/nfp/nfp_net_common.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c index 4fbda0eb4776..c763a5b3bd6b 100644 --- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c +++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c @@ -927,6 +927,9 @@ static void nfp_net_tx_complete(struct nfp_net_tx_ring *tx_ring) int fidx; int idx; + if (tx_ring->wr_p == tx_ring->rd_p) + return; + /* Work out how many descriptors have been transmitted */ qcp_rd_p = nfp_qcp_rd_ptr_read(tx_ring->qcp_q); @@ -1001,6 +1004,9 @@ static void nfp_net_xdp_complete(struct nfp_net_tx_ring *tx_ring) int idx, todo; u32 qcp_rd_p; + if (tx_ring->wr_p == tx_ring->rd_p) + return; + /* Work out how many descriptors have been transmitted */ qcp_rd_p = nfp_qcp_rd_ptr_read(tx_ring->qcp_q); -- 2.20.1