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Commit 73852e81 authored by Steven J. Magnani's avatar Steven J. Magnani Committed by David S. Miller
Browse files

NET_DMA: free skbs periodically 



Under NET_DMA, data transfer can grind to a halt when userland issues a
large read on a socket with a high RCVLOWAT (i.e., 512 KB for both).
This appears to be because the NET_DMA design queues up lots of memcpy
operations, but doesn't issue or wait for them (and thus free the
associated skbs) until it is time for tcp_recvmesg() to return.
The socket hangs when its TCP window goes to zero before enough data is
available to satisfy the read.

Periodically issue asynchronous memcpy operations, and free skbs for ones
that have completed, to prevent sockets from going into zero-window mode.

Signed-off-by: default avatarSteven J. Magnani <steve@digidescorp.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f5d410f2

net/ipv4/tcp.c

+43 −20
Original line number Diff line number Diff line
@@ -1254,6 +1254,39 @@ static void tcp_prequeue_process(struct sock *sk) 
	tp->ucopy.memory = 0;

}



#ifdef CONFIG_NET_DMA

static void tcp_service_net_dma(struct sock *sk, bool wait)

{

	dma_cookie_t done, used;

	dma_cookie_t last_issued;

	struct tcp_sock *tp = tcp_sk(sk);



	if (!tp->ucopy.dma_chan)

		return;



	last_issued = tp->ucopy.dma_cookie;

	dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);



	do {

		if (dma_async_memcpy_complete(tp->ucopy.dma_chan,

					      last_issued, &done,

					      &used) == DMA_SUCCESS) {

			/* Safe to free early-copied skbs now */

			__skb_queue_purge(&sk->sk_async_wait_queue);

			break;

		} else {

			struct sk_buff *skb;

			while ((skb = skb_peek(&sk->sk_async_wait_queue)) &&

			       (dma_async_is_complete(skb->dma_cookie, done,

						      used) == DMA_SUCCESS)) {

				__skb_dequeue(&sk->sk_async_wait_queue);

				kfree_skb(skb);

			}

		}

	} while (wait);

}

#endif



static inline struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)

{

	struct sk_buff *skb;
@@ -1546,6 +1579,10 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, 
			/* __ Set realtime policy in scheduler __ */

		}



#ifdef CONFIG_NET_DMA

		if (tp->ucopy.dma_chan)

			dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);

#endif

		if (copied >= target) {

			/* Do not sleep, just process backlog. */

			release_sock(sk);
@@ -1554,6 +1591,7 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, 
			sk_wait_data(sk, &timeo);



#ifdef CONFIG_NET_DMA

		tcp_service_net_dma(sk, false);  /* Don't block */

		tp->ucopy.wakeup = 0;

#endif
@@ -1633,6 +1671,9 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, 
						copied = -EFAULT;

					break;

				}



				dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);



				if ((offset + used) == skb->len)

					copied_early = 1;
@@ -1702,27 +1743,9 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, 
	}



#ifdef CONFIG_NET_DMA

	if (tp->ucopy.dma_chan) {

		dma_cookie_t done, used;



		dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);



		while (dma_async_memcpy_complete(tp->ucopy.dma_chan,

						 tp->ucopy.dma_cookie, &done,

						 &used) == DMA_IN_PROGRESS) {

			/* do partial cleanup of sk_async_wait_queue */

			while ((skb = skb_peek(&sk->sk_async_wait_queue)) &&

			       (dma_async_is_complete(skb->dma_cookie, done,

						      used) == DMA_SUCCESS)) {

				__skb_dequeue(&sk->sk_async_wait_queue);

				kfree_skb(skb);

			}

		}



		/* Safe to free early-copied skbs now */

		__skb_queue_purge(&sk->sk_async_wait_queue);

	tcp_service_net_dma(sk, true);  /* Wait for queue to drain */

	tp->ucopy.dma_chan = NULL;

	}



	if (tp->ucopy.pinned_list) {

		dma_unpin_iovec_pages(tp->ucopy.pinned_list);

		tp->ucopy.pinned_list = NULL;