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Commit a41ef053 authored by Dave Jiang's avatar Dave Jiang Committed by Jon Mason
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NTB: Default to CPU memcpy for performance 



Disable DMA usage by default, since the CPU provides much better
performance with write combining.  Provide a module parameter to enable
DMA usage when offloading the memcpy is preferred.

Signed-off-by: default avatarDave Jiang <dave.jiang@intel.com>
Signed-off-by: default avatarAllen Hubbe <Allen.Hubbe@emc.com>
Signed-off-by: default avatarJon Mason <jdmason@kudzu.us>
parent 06917f75

drivers/ntb/ntb_transport.c

+13 −4
Original line number Diff line number Diff line
@@ -88,6 +88,10 @@ static unsigned int copy_bytes = 1024; 
module_param(copy_bytes, uint, 0644);

MODULE_PARM_DESC(copy_bytes, "Threshold under which NTB will use the CPU to copy instead of DMA");



static bool use_dma;

module_param(use_dma, bool, 0644);

MODULE_PARM_DESC(use_dma, "Use DMA engine to perform large data copy");



static struct dentry *nt_debugfs_dir;



struct ntb_queue_entry {
@@ -1589,10 +1593,15 @@ ntb_transport_create_queue(void *data, struct device *client_dev, 
	dma_cap_zero(dma_mask);

	dma_cap_set(DMA_MEMCPY, dma_mask);



	if (use_dma) {

		qp->dma_chan = dma_request_channel(dma_mask, ntb_dma_filter_fn,

						   (void *)(unsigned long)node);

		if (!qp->dma_chan)

		dev_info(&pdev->dev, "Unable to allocate DMA channel, using CPU instead\n");

			dev_info(&pdev->dev, "Unable to allocate DMA channel\n");

	} else {

		qp->dma_chan = NULL;

	}

	dev_dbg(&pdev->dev, "Using %s memcpy\n", qp->dma_chan ? "DMA" : "CPU");



	for (i = 0; i < NTB_QP_DEF_NUM_ENTRIES; i++) {

		entry = kzalloc_node(sizeof(*entry), GFP_ATOMIC, node);