From: John Feeney <jfeeney@redhat.com>
Date: Thu, 17 Jan 2008 14:17:33 -0500
Subject: [misc] ioat: support for 1.9
Message-id: 478FA9CD.8070108@redhat.com
O-Subject: Re: [RHEL-5.2 PATCH] Support for I/O AT level 1.9
Bugzilla: 209411

bz209411
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=209411
ioatdma 1.8 or higher required for better I/OAT performance

Solution:
According to Intel, there are two upstream -mm patches:

   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.

and

   ioatdma: Push pending transactions to hardware more frequently
   Every 20 descriptors turns out to be to few append commands with
   newer/faster CPUs.  Pushing every 4 still cuts down on MMIO writes to an
   acceptable level without letting the DMA engine run out of work.

Both of these patches are listed in the bugzilla and were backported
to RHEL-5.1.

Testing:
I ported the Dell patch to the RHEL 5.1 code base and built a release
in brew. Unfortunately, still waiting for test results from Dell but I
have
posted so it can get posted before the deadline.

Acks would be appreciated. Thanks.

After discussing this with Linda, I promised to provide a
patch for what I believe you guys want, the parameter
and a global ioat_pending_level variable so the high water
mark is configurable. This removes just this functionality
(5 lines) from 7bb67c14fd3778504fb77da30ce11582336dfced
and leaves ioatdma.c and the remaining 6 files of that
upstream patch untouched.

Acked-by: Pete Zaitcev <zaitcev@redhat.com>
Acked-by: "David S. Miller" <davem@redhat.com>

diff --git a/drivers/dma/ioatdma.c b/drivers/dma/ioatdma.c
index dc29723..2f30270 100644
--- a/drivers/dma/ioatdma.c
+++ b/drivers/dma/ioatdma.c
@@ -40,6 +40,11 @@
 #define to_ioat_device(dev) container_of(dev, struct ioat_device, common)
 #define to_ioat_desc(lh) container_of(lh, struct ioat_desc_sw, node)
 
+static int ioat_pending_level = 4;
+module_param(ioat_pending_level, int, 0644);
+MODULE_PARM_DESC(ioat_pending_level,
+		 "high-water mark for pushing ioat descriptors (default: 4)");
+
 /* internal functions */
 static int __devinit ioat_probe(struct pci_dev *pdev, const struct pci_device_id *ent);
 static void __devexit ioat_remove(struct pci_dev *pdev);
@@ -310,7 +315,8 @@ static dma_cookie_t do_ioat_dma_memcpy(struct ioat_dma_chan *ioat_chan,
 	list_splice_init(&new_chain, ioat_chan->used_desc.prev);
 
 	ioat_chan->pending += desc_count;
-	if (ioat_chan->pending >= 20) {
+	if (ioat_chan->pending >= ioat_pending_level)
+	{
 		append = 1;
 		ioat_chan->pending = 0;
 	}
@@ -820,7 +826,7 @@ static void __devexit ioat_remove(struct pci_dev *pdev)
 }
 
 /* MODULE API */
-MODULE_VERSION("1.7");
+MODULE_VERSION("1.9");
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Intel Corporation");
 
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 05bb4ce..f3fd4f1 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1108,6 +1108,7 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	long timeo;
 	struct task_struct *user_recv = NULL;
 	int copied_early = 0;
+	struct sk_buff *skb;
 
 	lock_sock(sk);
 
@@ -1134,16 +1135,25 @@ 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) &&
-	    !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);
-	} else
-		preempt_enable_no_resched();
+	skb = skb_peek_tail(&sk->sk_receive_queue);
+	{
+		int available = 0;
+		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);
+		} else {
+			preempt_enable_no_resched();
+		}
+	}
 #endif
 
 	do {
-		struct sk_buff *skb;
 		u32 offset;
 
 		/* Are we at urgent data? Stop if we have read anything or have SIGURG pending. */
@@ -1431,7 +1441,6 @@ 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);