From f89271da32bc1a636cf4eb078e615930886cd013 Mon Sep 17 00:00:00 2001 From: Eli Cohen Date: Mon, 14 Jul 2008 23:48:44 -0700 Subject: [PATCH] IPoIB: Copy small received SKBs in connected mode The connected mode implementation in the IPoIB driver has a large overhead in the way SKBs are handled in the receive flow. It usually allocates an SKB with as big as was used in the currently received SKB and moves unused fragments from the old SKB to the new one. This involves a loop on all the remaining fragments and incurs overhead on the CPU. This patch, for small SKBs, allocates an SKB just large enough to contain the received data and copies to it the data from the received SKB. The newly allocated SKB is passed to the stack and the old SKB is reposted. When running netperf, UDP small messages, without this pach I get: UDP UNIDIRECTIONAL SEND TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 14.4.3.178 (14.4.3.178) port 0 AF_INET Socket Message Elapsed Messages Size Size Time Okay Errors Throughput bytes bytes secs # # 10^6bits/sec 114688 128 10.00 5142034 0 526.31 114688 10.00 1130489 115.71 With this patch I get both send and receive at ~315 mbps. The reason that send performance actually slows down is as follows: When using this patch, the overhead of the CPU for handling RX packets is dramatically reduced. As a result, we do not experience RNR NAK messages from the receiver which cause the connection to be closed and reopened again; when the patch is not used, the receiver cannot handle the packets fast enough so there is less time to post new buffers and hence the mentioned RNR NACKs. So what happens is that the application *thinks* it posted a certain number of packets for transmission but these packets are flushed and do not really get transmitted. Since the connection gets opened and closed many times, each time netperf gets the CPU time that otherwise would have been given to IPoIB to actually transmit the packets. This can be verified when looking at the port counters -- the output of ifconfig and the oputput of netperf (this is for the case without the patch): tx packets ========== port counter: 1,543,996 ifconfig: 1,581,426 netperf: 5,142,034 rx packets ========== netperf 1,1304,089 Signed-off-by: Eli Cohen --- drivers/infiniband/ulp/ipoib/ipoib.h | 1 + drivers/infiniband/ulp/ipoib/ipoib_cm.c | 19 +++++++++++++++++++ drivers/infiniband/ulp/ipoib/ipoib_main.c | 6 ++++++ 3 files changed, 26 insertions(+) diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h index 0dcbab3203c9..8754b364f229 100644 --- a/drivers/infiniband/ulp/ipoib/ipoib.h +++ b/drivers/infiniband/ulp/ipoib/ipoib.h @@ -95,6 +95,7 @@ enum { IPOIB_MCAST_FLAG_ATTACHED = 3, MAX_SEND_CQE = 16, + IPOIB_CM_COPYBREAK = 256, }; #define IPOIB_OP_RECV (1ul << 31) diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c index 91c959299910..6223fc39af70 100644 --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c @@ -523,6 +523,7 @@ void ipoib_cm_handle_rx_wc(struct net_device *dev, struct ib_wc *wc) u64 mapping[IPOIB_CM_RX_SG]; int frags; int has_srq; + struct sk_buff *small_skb; ipoib_dbg_data(priv, "cm recv completion: id %d, status: %d\n", wr_id, wc->status); @@ -577,6 +578,23 @@ void ipoib_cm_handle_rx_wc(struct net_device *dev, struct ib_wc *wc) } } + if (wc->byte_len < IPOIB_CM_COPYBREAK) { + int dlen = wc->byte_len; + + small_skb = dev_alloc_skb(dlen + 12); + if (small_skb) { + skb_reserve(small_skb, 12); + ib_dma_sync_single_for_cpu(priv->ca, rx_ring[wr_id].mapping[0], + dlen, DMA_FROM_DEVICE); + skb_copy_from_linear_data(skb, small_skb->data, dlen); + ib_dma_sync_single_for_device(priv->ca, rx_ring[wr_id].mapping[0], + dlen, DMA_FROM_DEVICE); + skb_put(small_skb, dlen); + skb = small_skb; + goto copied; + } + } + frags = PAGE_ALIGN(wc->byte_len - min(wc->byte_len, (unsigned)IPOIB_CM_HEAD_SIZE)) / PAGE_SIZE; @@ -599,6 +617,7 @@ void ipoib_cm_handle_rx_wc(struct net_device *dev, struct ib_wc *wc) skb_put_frags(skb, IPOIB_CM_HEAD_SIZE, wc->byte_len, newskb); +copied: skb->protocol = ((struct ipoib_header *) skb->data)->proto; skb_reset_mac_header(skb); skb_pull(skb, IPOIB_ENCAP_LEN); diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c index f217b1edd0ac..bfe1dbf99207 100644 --- a/drivers/infiniband/ulp/ipoib/ipoib_main.c +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c @@ -1302,6 +1302,12 @@ static int __init ipoib_init_module(void) ipoib_max_conn_qp = min(ipoib_max_conn_qp, IPOIB_CM_MAX_CONN_QP); #endif + /* + * When copying small received packets, we only copy from the + * linear data part of the SKB, so we rely on this condition. + */ + BUILD_BUG_ON(IPOIB_CM_COPYBREAK > IPOIB_CM_HEAD_SIZE); + ret = ipoib_register_debugfs(); if (ret) return ret; -- 2.20.1