Subject: Re: [PATCH v2 3/4] I/OAT: tcp_dma_copybreak default value dependant onI/OAT version

From: Dan Williams <[email-masked]>
Date: Fri, 18 Jul 2008 11:54:14 -0700

On Fri, 2008-07-18 at 08:29 -0700, Sosnowski, Maciej wrote:
> I/OAT DMA performance tuning showed different optimal values
> of tcp_dma_copybreak for different I/OAT versions
> (4096 for 1.2 and 2048 for 2.0).
> This patch lets ioatdma driver set tcp_dma_copybreak value
> according to these results.
> 
> Signed-off-by: Maciej Sosnowski <[email-masked]>

Let's kill some ifdef's... how about the following instead?

diff --git a/drivers/dma/ioat_dma.c b/drivers/dma/ioat_dma.c
index 171cad6..1c0dafc 100644
--- a/drivers/dma/ioat_dma.c
+++ b/drivers/dma/ioat_dma.c
@@ -1330,6 +1330,8 @@ struct ioatdma_device *ioat_dma_probe(struct pci_dev *pdev,
 	if (err)
 		goto err_self_test;
 
+	ioat_set_tcp_copy_break(device);
+
 	dma_async_device_register(&device->common);
 
 	return device;
diff --git a/drivers/dma/ioatdma.h b/drivers/dma/ioatdma.h
index f2c7fed..23e3196 100644
--- a/drivers/dma/ioatdma.h
+++ b/drivers/dma/ioatdma.h
@@ -27,6 +27,7 @@
 #include <linux/dmapool.h>
 #include <linux/cache.h>
 #include <linux/pci_ids.h>
+#include <net/tcp.h>
 
 #define IOAT_DMA_VERSION  "2.04"
 
@@ -121,6 +122,20 @@ struct ioat_desc_sw {
 	struct dma_async_tx_descriptor async_tx;
 };
 
+static inline void ioat_set_tcp_copy_break(struct ioatdma_device *dev)
+{
+	#ifdef CONFIG_NET_DMA
+	switch (dev->version) {
+	case IOAT_VER_1_2:
+		sysctl_tcp_dma_copybreak = 4096;
+		break;
+	case IOAT_VER_2_0:
+		sysctl_tcp_dma_copybreak = 2048;
+		break;
+	}
+	#endif
+}
+
 #if defined(CONFIG_INTEL_IOATDMA) || defined(CONFIG_INTEL_IOATDMA_MODULE)
 struct ioatdma_device *ioat_dma_probe(struct pci_dev *pdev,
 				      void __iomem *iobase);
diff --git a/net/core/user_dma.c b/net/core/user_dma.c
index 0ad1cd5..de76050 100644
--- a/net/core/user_dma.c
+++ b/net/core/user_dma.c
@@ -34,6 +34,7 @@
 #define NET_DMA_DEFAULT_COPYBREAK 4096
 
 int sysctl_tcp_dma_copybreak = NET_DMA_DEFAULT_COPYBREAK;
+EXPORT_SYMBOL(sysctl_tcp_dma_copybreak);
 
 /**
  *	dma_skb_copy_datagram_iovec - Copy a datagram to an iovec.