From 2b1244a43be97f504494b557a7f7a65fe0d00dba Mon Sep 17 00:00:00 2001 From: Chris Leech Date: Thu, 8 Mar 2007 09:57:36 -0800 Subject: [PATCH] I/OAT: Only offload copies for TCP when there will be a context switch The performance wins come with having the DMA copy engine doing the copies in parallel with the context switch. If there is enough data ready on the socket at recv time just use a regular copy. Signed-off-by: Chris Leech --- net/ipv4/tcp.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 450f44bb2c..0eb7cf1002 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1116,6 +1116,8 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, long timeo; struct task_struct *user_recv = NULL; int copied_early = 0; + int available = 0; + struct sk_buff *skb; lock_sock(sk); @@ -1142,7 +1144,11 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, #ifdef CONFIG_NET_DMA tp->ucopy.dma_chan = NULL; preempt_disable(); - if ((len > sysctl_tcp_dma_copybreak) && !(flags & MSG_PEEK) && + skb = skb_peek_tail(&sk->sk_receive_queue); + if (skb) + available = TCP_SKB_CB(skb)->seq + skb->len - (*seq); + if ((available < target) && + (len > sysctl_tcp_dma_copybreak) && !(flags & MSG_PEEK) && !sysctl_tcp_low_latency && __get_cpu_var(softnet_data).net_dma) { preempt_enable_no_resched(); tp->ucopy.pinned_list = dma_pin_iovec_pages(msg->msg_iov, len); @@ -1151,7 +1157,6 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, #endif do { - struct sk_buff *skb; u32 offset; /* Are we at urgent data? Stop if we have read anything or have SIGURG pending. */ @@ -1439,7 +1444,6 @@ skip_copy: #ifdef CONFIG_NET_DMA if (tp->ucopy.dma_chan) { - struct sk_buff *skb; dma_cookie_t done, used; dma_async_memcpy_issue_pending(tp->ucopy.dma_chan); -- 2.20.1